fix: add check for blank content before loading workflow context from file

Author: sharrlotte

src/main/java/mindustrytool/workflow/Workflow.java

@@ -115,8 +115,10 @@ public void writeWorkflowData(JsonNode data) {
 
     private void loadWorkflowFromFile() {
         String content = WORKFLOW_FILE.readString();
-        context = JsonUtils.readJsonAsClass(content, WorkflowContext.class);
-        load(context);
+        if (!content.isBlank()) {
+            context = JsonUtils.readJsonAsClass(content, WorkflowContext.class);
+            load(context);
+        }
     }
 
     private void writeWorkflowToFile() {