fix: LoadingSnackBar consistently remains visible until the upload is complete

- Adjusted the `SendFileDialogState` file to ensure that the `showLoadingSnackBar` remains visible throughout the file upload process.
- the SnackBar is cleared only after the image/file is uploaded and displayed in the chat.

Signed-off-by: JaWeee <dohoanggiahuy310703@gmail.com>

lib/pages/chat/send_file_dialog.dart

@@ -88,8 +88,6 @@ class SendFileDialogState extends State<SendFileDialog> {
               widget.files.length,
             ),
           );
-        } else {
-          scaffoldMessenger.clearSnackBars();
         }
 
         try {