Guard dropEvent against empty URL list

Calling constLast() on an empty QList crashes. Although dragEnterEvent
only accepts drops with hasUrls(), the MIME data could theoretically
change between the drag-enter and drop events, so guard explicitly.

https://claude.ai/code/session_01KvuREfVMg7MnzkpLBg8NVz

Author: claude

src/dialogs/importmbcdialog.cpp

@@ -233,7 +233,13 @@ void ImportMbcDialog::dragEnterEvent(QDragEnterEvent* e)
 
 void ImportMbcDialog::dropEvent(QDropEvent* e)
 {
-    const QString filename(e->mimeData()->urls().constLast().toLocalFile());
+    const QList<QUrl> urls = e->mimeData()->urls();
+    if (urls.isEmpty())
+    {
+        return;
+    }
+
+    const QString filename(urls.constLast().toLocalFile());
 
     _pUi->lineMbcfile->setText(filename);
     _pGuiModel->setLastMbcImportedFile(filename);