Fixes grid column type concat (#4476)

* Fixes grid column type `concat`

* removed useless test

Author: sreichel

app/code/core/Mage/Adminhtml/Block/Widget/Grid.php

@@ -345,7 +345,10 @@ public function addColumnDefaultData(array $column): array
     {
         $config = $this->getConfigDefaultColumnSettings();
         $columnHasIndex = array_key_exists('index', $column);
-        if ($columnHasIndex && array_key_exists($column['index'], $config['index'])) {
+        if ($columnHasIndex &&
+            !is_array($column['index']) &&
+            array_key_exists($column['index'], $config['index'])
+        ) {
             $column += $config['index'][$column['index']];
         }
 

app/code/core/Mage/Adminhtml/etc/config.xml

@@ -267,6 +267,9 @@
                         <sortable>false</sortable>
                         <width>40</width>
                     </action>
+                    <concat>
+                        <separator> </separator>
+                    </concat>
                     <currency>
                         <align>right</align>
                         <index>price</index>

tests/unit/Mage/Adminhtml/Block/Widget/GridTest.php

@@ -72,6 +72,17 @@ public function provideAddColumnDefaultData(): Generator
                 'type' => 'text',
             ],
         ];
+        yield 'index array - ref #4475' => [
+            [
+                'index' => ['firstname', 'lastname'],
+                'type' => 'concat',
+                'separator' => ' ',
+            ],
+            [
+                'index'     => ['firstname', 'lastname'],
+                'type'      => 'concat',
+            ],
+        ];
         yield 'type action' => [
             [
                 'type' => 'action',