fixed a bug

src/components/VocabularyStudy.tsx

@@ -642,13 +642,17 @@ const VocabularyStudy: React.FC = () => {
       answerSubmittingRef.current = false;
       return;
     }
-    if (testType === 'multiple-choice' && options.length > 0 && options.every(option => option.token !== userAnswer)) {
+    const normalizedUserAnswer = userAnswer.trim();
+    if (!normalizedUserAnswer) {
+      answerSubmittingRef.current = false;
+      return;
+    }
+    if (testType === 'multiple-choice' && options.length > 0 && options.every(option => option.token !== normalizedUserAnswer)) {
       answerSubmittingRef.current = false;
       message.warning('请选择一个选项后再提交');
       return;
     }
     const submittedAt = Date.now();
-    const normalizedUserAnswer = userAnswer.trim();
     const answerProof = buildAnswerProof(
       testAttemptId,
       currentQuestion.questionToken,
@@ -1411,6 +1415,7 @@ const VocabularyStudy: React.FC = () => {
                       style={{ marginBottom: 15, userSelect: 'none', WebkitUserSelect: 'none' }}
                       onPressEnter={e => {
                         e.stopPropagation();
+                        if (!userAnswer.trim() || showAnswer) return;
                         submitAnswer();
                       }}
                       autoFocus
@@ -1444,7 +1449,7 @@ const VocabularyStudy: React.FC = () => {
                   <Button 
                     type="primary" 
                     onClick={submitAnswer}
-                    disabled={!userAnswer || showAnswer}
+                    disabled={!userAnswer.trim() || showAnswer}
                     style={{ width: '100%' }}
                   >
                     提交答案