file chooser: Avoid nonworking search+save combinations

file chooser: Avoid nonworking search+save combinations

With the location entry up in the header bar in save mode, we can
end up with the search model being in use when the user types in
the location entry. In this case, we don't make the Save button
sensitive as we should.

Having two entries in the dialog is somewhat confusing anyway,
so just stop the search when the user starts typing in the location
entry.

https://bugzilla.gnome.org/show_bug.cgi?id=761757