Fix frame position on non-seekable sources.
Fix frame position on non-seekable sources.

This was discovered trying to use YADIF deinterlace on a non-seekable
interlaced file.

siddharudh/mlt,xzhavilla/mlt,xzhavilla/mlt,j-b-m/mlt,mltframework/mlt,anba8005/mlt,siddharudh/mlt,mltframework/mlt,j-b-m/mlt,siddharudh/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,xzhavilla/mlt,anba8005/mlt,j-b-m/mlt,mltframework/mlt,anba8005/mlt,j-b-m/mlt,xzhavilla/mlt,anba8005/mlt,siddharudh/mlt,j-b-m/mlt,siddharudh/mlt,xzhavilla/mlt,xzhavilla/mlt,xzhavilla/mlt,j-b-m/mlt,siddharudh/mlt,mltframework/mlt,j-b-m/mlt,xzhavilla/mlt,j-b-m/mlt,siddharudh/mlt,mltframework/mlt,siddharudh/mlt,mltframework/mlt,anba8005/mlt,siddharudh/mlt,mltframework/mlt,anba8005/mlt,mltframework/mlt,anba8005/mlt,xzhavilla/mlt,anba8005/mlt,anba8005/mlt,j-b-m/mlt