vaapivideomemory: increment map counter only if succeeded
vaapivideomemory: increment map counter only if succeeded

Previously the frame map counter increased independently if the map succeeded
or not. This leaded to critical messages and crashes if the frame was unable
to be mapped, but the counter increased.

This patch increases the map counter only if the map operation occurred.

https://bugzilla.gnome.org/show_bug.cgi?id=773939

01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi