Enhance _extractVocabFromExercises method for robust input handling

- Added checks to ensure the exercises parameter is an array, with console warnings for null, undefined, or non-array inputs.
- Implemented logic to convert non-array objects with a length property into arrays, improving flexibility in handling various input types.
- Enhanced error logging to provide clearer insights when input conversion fails, aiding in debugging and user feedback.

frontend/src/views/social/VocabLessonView.vue

@@ -414,9 +414,28 @@ export default {
       }
     },
     _extractVocabFromExercises(exercises) {
+      // Sicherstellen, dass exercises ein Array ist
+      if (!exercises) {
+        console.warn('[_extractVocabFromExercises] exercises ist null/undefined:', exercises);
+        return [];
+      }
+      
+      // Konvertiere zu Array falls nötig
+      let exercisesArray = exercises;
+      if (!Array.isArray(exercises)) {
+        console.warn('[_extractVocabFromExercises] exercises ist kein Array, versuche zu konvertieren:', exercises);
+        // Falls es ein Objekt mit length ist, versuche es zu konvertieren
+        if (typeof exercises === 'object' && exercises.length !== undefined) {
+          exercisesArray = Array.from(exercises);
+        } else {
+          console.error('[_extractVocabFromExercises] Kann exercises nicht zu Array konvertieren:', exercises);
+          return [];
+        }
+      }
+      
       const vocabMap = new Map();
       
-      exercises.forEach((exercise, idx) => {
+      exercisesArray.forEach((exercise, idx) => {
           try {
             console.log(`[importantVocab] Verarbeite Übung ${idx + 1}:`, exercise.title);
             // Extrahiere aus questionData