main_window: don't crash picking file from smb/gvfs
Application crashes when trying to select a file on GVFS (smb://, etc)
Traceback (most recent call last):
File "/nix/store/255dn759x2ngl057b2d5l671rhfpb6vz-gnome-passwordsafe-4.0/lib/python3.8/site-packages/passwordsafe/main_window.py", line 330, in open_filechooser
file_mime_type = Gio.content_type_get_mime_type(file_content_type)
TypeError: Argument 0 does not allow None as a value
This seems to be because Gio.FileInfo.get_content_type()
checks only for standard::content-type
attribute, but files on GVFS network filesystems only have standard::fast-content-type
to save bandwidth or something so it returns None