udisks2: Fix crash when mounting encrypted volume
udisks2: Fix crash when mounting encrypted volume

Code handling external unlocks during mount operation was added by the
commit beea21e recently. Unfortunately, it may cause crashes due to
accessing already freed memory, because gvfs_udisks2_volume_monitor_update
waits for pending dbus messages using udisks_client_settle, thus another
main context iteration may happen (i.e. mount operation may finish and
mount data may be freed) before accessing mount data pointer. The mount
data pointer has to be obtained after gvfs_udisks2_volume_monitor_update
call in order to fix this crashes.

https://bugzilla.gnome.org/show_bug.cgi?id=765146

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs