Fix composite using wrong B frame scaling.
Fix composite using wrong B frame scaling.

This could happen when the caller of mlt_frame_get_image supplied 0 for
width and height. For example, Kdenlive's GL output with the sdl_audio
consumer with real_time > 1 and paused.

anba8005/mlt,siddharudh/mlt,j-b-m/mlt,gmarco/mlt-orig,anba8005/mlt,mltframework/mlt,zzhhui/mlt,xzhavilla/mlt,ttill/MLT,mltframework/mlt,gmarco/mlt-orig,siddharudh/mlt,zzhhui/mlt,zzhhui/mlt,ttill/MLT-roto-tracking,ttill/MLT-roto-tracking,wideioltd/mlt,anba8005/mlt,ttill/MLT,j-b-m/mlt,ttill/MLT,wideioltd/mlt,xzhavilla/mlt,ttill/MLT-roto-tracking,ttill/MLT-roto-tracking,ttill/MLT,xzhavilla/mlt,siddharudh/mlt,wideioltd/mlt,gmarco/mlt-orig,siddharudh/mlt,ttill/MLT-roto-tracking,wideioltd/mlt,gmarco/mlt-orig,ttill/MLT-roto-tracking,zzhhui/mlt,ttill/MLT,ttill/MLT,wideioltd/mlt,ttill/MLT,anba8005/mlt,mltframework/mlt,j-b-m/mlt,zzhhui/mlt,j-b-m/mlt,siddharudh/mlt,xzhavilla/mlt,j-b-m/mlt,j-b-m/mlt,xzhavilla/mlt,anba8005/mlt,gmarco/mlt-orig,xzhavilla/mlt,anba8005/mlt,wideioltd/mlt,zzhhui/mlt,mltframework/mlt,j-b-m/mlt,ttill/MLT,mltframework/mlt,gmarco/mlt-orig,anba8005/mlt,j-b-m/mlt,xzhavilla/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,gmarco/mlt-orig,gmarco/mlt-orig,siddharudh/mlt,ttill/MLT,mltframework/mlt,zzhhui/mlt,ttill/MLT-roto-tracking,wideioltd/mlt,siddharudh/mlt,xzhavilla/mlt,mltframework/mlt,zzhhui/mlt,ttill/MLT-roto-tracking,ttill/MLT-roto-tracking,j-b-m/mlt,wideioltd/mlt,mltframework/mlt,wideioltd/mlt,xzhavilla/mlt,siddharudh/mlt,gmarco/mlt-orig,zzhhui/mlt,anba8005/mlt,siddharudh/mlt,anba8005/mlt