Fix for DescribeWorkflow (#773)

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## What was changed
<!-- Describe what has changed in this PR -->
Check if extended info is not nil.

## Why?
<!-- Tell your future self why have you made these changes -->
#771
Code assumes that some extended info exists in proto. Which is not true
for older server versions..

Author: ychebotarev

temporalcli/commands.workflow_view.go

@@ -102,49 +102,56 @@ func (c *TemporalWorkflowDescribeCommand) run(cctx *CommandContext, args []strin
 
 	cctx.Printer.Println(color.MagentaString("Execution Info:"))
 	info := resp.WorkflowExecutionInfo
-	extendedInfo := resp.WorkflowExtendedInfo
 	_ = cctx.Printer.PrintStructured(struct {
-		WorkflowId              string
-		RunId                   string
-		Type                    string
-		Namespace               string
-		TaskQueue               string
-		AssignedBuildId         string
-		StartTime               time.Time
-		CloseTime               time.Time                  `cli:",cardOmitEmpty"`
-		ExecutionTime           time.Time                  `cli:",cardOmitEmpty"`
-		Memo                    map[string]*common.Payload `cli:",cardOmitEmpty"`
-		SearchAttributes        map[string]*common.Payload `cli:",cardOmitEmpty"`
-		StateTransitionCount    int64
-		HistoryLength           int64
-		HistorySize             int64
-		ExecutionExpirationTime time.Time `cli:",cardOmitEmpty"`
-		RunExpirationTime       time.Time `cli:",cardOmitEmpty"`
-		CancelRequested         bool
-		LastResetTime           time.Time `cli:",cardOmitEmpty"`
-		OriginalStartTime       time.Time `cli:",cardOmitEmpty"`
+		WorkflowId           string
+		RunId                string
+		Type                 string
+		Namespace            string
+		TaskQueue            string
+		AssignedBuildId      string
+		StartTime            time.Time
+		CloseTime            time.Time                  `cli:",cardOmitEmpty"`
+		ExecutionTime        time.Time                  `cli:",cardOmitEmpty"`
+		Memo                 map[string]*common.Payload `cli:",cardOmitEmpty"`
+		SearchAttributes     map[string]*common.Payload `cli:",cardOmitEmpty"`
+		StateTransitionCount int64
+		HistoryLength        int64
+		HistorySize          int64
 	}{
-		WorkflowId:              info.Execution.WorkflowId,
-		RunId:                   info.Execution.RunId,
-		Type:                    info.Type.GetName(),
-		Namespace:               c.Parent.Namespace,
-		TaskQueue:               info.TaskQueue,
-		AssignedBuildId:         info.GetAssignedBuildId(),
-		StartTime:               timestampToTime(info.StartTime),
-		CloseTime:               timestampToTime(info.CloseTime),
-		ExecutionTime:           timestampToTime(info.ExecutionTime),
-		Memo:                    info.Memo.GetFields(),
-		SearchAttributes:        info.SearchAttributes.GetIndexedFields(),
-		StateTransitionCount:    info.StateTransitionCount,
-		HistoryLength:           info.HistoryLength,
-		HistorySize:             info.HistorySizeBytes,
-		ExecutionExpirationTime: timestampToTime(extendedInfo.ExecutionExpirationTime),
-		RunExpirationTime:       timestampToTime(extendedInfo.RunExpirationTime),
-		CancelRequested:         extendedInfo.CancelRequested,
-		LastResetTime:           timestampToTime(extendedInfo.LastResetTime),
-		OriginalStartTime:       timestampToTime(extendedInfo.OriginalStartTime),
+		WorkflowId:           info.Execution.WorkflowId,
+		RunId:                info.Execution.RunId,
+		Type:                 info.Type.GetName(),
+		Namespace:            c.Parent.Namespace,
+		TaskQueue:            info.TaskQueue,
+		AssignedBuildId:      info.GetAssignedBuildId(),
+		StartTime:            timestampToTime(info.StartTime),
+		CloseTime:            timestampToTime(info.CloseTime),
+		ExecutionTime:        timestampToTime(info.ExecutionTime),
+		Memo:                 info.Memo.GetFields(),
+		SearchAttributes:     info.SearchAttributes.GetIndexedFields(),
+		StateTransitionCount: info.StateTransitionCount,
+		HistoryLength:        info.HistoryLength,
+		HistorySize:          info.HistorySizeBytes,
 	}, printer.StructuredOptions{})
 
+	extendedInfo := resp.WorkflowExtendedInfo
+	if extendedInfo != nil {
+		cctx.Printer.Println(color.MagentaString("Extended Execution Info:"))
+		_ = cctx.Printer.PrintStructured(struct {
+			CancelRequested         bool
+			ExecutionExpirationTime time.Time `cli:",cardOmitEmpty"`
+			RunExpirationTime       time.Time `cli:",cardOmitEmpty"`
+			LastResetTime           time.Time `cli:",cardOmitEmpty"`
+			OriginalStartTime       time.Time `cli:",cardOmitEmpty"`
+		}{
+			CancelRequested:         extendedInfo.CancelRequested,
+			ExecutionExpirationTime: timestampToTime(extendedInfo.ExecutionExpirationTime),
+			RunExpirationTime:       timestampToTime(extendedInfo.RunExpirationTime),
+			LastResetTime:           timestampToTime(extendedInfo.LastResetTime),
+			OriginalStartTime:       timestampToTime(extendedInfo.OriginalStartTime),
+		}, printer.StructuredOptions{})
+	}
+
 	staticSummary := resp.GetExecutionConfig().GetUserMetadata().GetSummary()
 	staticDetails := resp.GetExecutionConfig().GetUserMetadata().GetDetails()
 	if len(staticSummary.GetData()) > 0 || len(staticDetails.GetData()) > 0 {