[Linux] Multiple warnings about importing a corrupted MusicXML file when opening from QFiledialog

Steps:
1- Open MuseScore; File -> Open;
2- In the browsing window, navigate to the folder containing the file in attachment (not 100% valid MuscXML);
3- Click (once) on the file; a warning about the file being not valid is displayed; click "yes" or "no";
4- Click the "Open" button; the warning is displayed again before loading the score.
Note that each time step -3- is repeated, the warning is displayed.

This happens under Linux, where the open dialog displays score previews and thumbnails are generated on-the-fly for score files not containing a preview.

Linux Mint, commit f4f19e9f3