Handle store state updates when moving documents

- Add null check to prevent error when evaluation is not part of this social work

src/Bundle/ChillPersonBundle/Resources/public/vuejs/AccompanyingCourseWorkEdit/store.js

@@ -326,9 +326,11 @@ const store = createStore({
         (e) => e.id === evaluationDest.id,
       );
 
-      // add document to chosen evaluation
-      document.key = evaluationB.documents.length + 1;
-      evaluationB.documents.splice(0, 0, document);
+      if (evaluationB) {
+        // add document to chosen evaluation if evaluation is part of the same social work
+        document.key = evaluationB.documents.length + 1;
+        evaluationB.documents.splice(0, 0, document);
+      }
 
       // remove document from original evaluation
       const indexToRemove = evaluationA.documents.findIndex(