Fix big memory leak in framebuffer producer.
Fix big memory leak in framebuffer producer.

This fix is for kdenlive bug 898. This was due to allocating a frame in
get_frame that might not get closed by a skipped call to get_image. This
skipping can happen when using realtime mode (frame dropping).

Signed-off-by: Dan Dennedy <2591e5f46f28d303f9dc027d475a5c60d8dea17a@dennedy.org>

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