Fix fields cannot be added on opportunity board if no field are present

packages/twenty-front/src/modules/object-record/record-index/options/hooks/useRecordIndexOptionsForBoard.ts

@@ -153,7 +153,7 @@ export const useRecordIndexOptionsForBoard = ({
           ...recordIndexFieldDefinitions,
           {
             ...correspondingFieldDefinition,
-            position: lastVisibleBoardField.position + 1,
+            position: (lastVisibleBoardField?.position || 0) + 1,
             isVisible: true,
           },
         ];