Fix crash when window is closed before finishing mount operation
Fix crash when window is closed before finishing mount operation

Fixes https://github.com/lxqt/libfm-qt/issues/441

The explanation is in the code comment. The crash can happen only with bad mounts (like MTP); usually, the user can't close the window before the mount operation is finished.

lxde/libfm-qt,lxde/libfm-qt