Allowing for correctly saving the gallery width setting (Bug #1366622)

Currently it checks what width it should be on rendering but it
should also do this on saving to make sure a width of 0 is not set.

Change-Id: I7837c3120fa29e2a2dc5c9c63301dfa4543428a4
Signed-off-by: Bob Lyon <bob@katipo.co.nz>