While opening folders in SvtFileView using doubleclick,
sometimes GtkSalFrame::gestureLongPress method is
executed with a null frame pointer and LO crashes.
I noticed this only with remote dirs, probably this
bug occurs only when the doubleclick handler routine
takes a lot of time.

(cherry picked from commit db33c785)

Change-Id: I432046994b3e1662bd7e499681bd20e9696b2d52
Reviewed-on: https://gerrit.libreoffice.org/18571Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>