We can only remove the logo if it is inside the picture. We need at
least one pixel around the logo area for interpolation.

Fixes ticket #5527 (Delogo crash with x=0 and/or y=0).
Signed-off-by: Jean Delvare <jdelvare@suse.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>