quartz: Try creating the file reader from the filter source first before falling back to the generic async file reader.

quartz: Make mpeg splitter keep track of play position and keep last sample if sending was not successful.

This fixes data discontinuities that earlier occured after a
stop/pause command or the downright rejection of a sample (S_FALSE).

This should fix the problem that in LoadLocation SFLAG_INTEXTURE path gl calls 
can be made without activating context, due to isInDraw checks.

Strictly speaking this is redundant because the UnLoad before did the
job, but if we mess with the allocated memory we have to tell the
surface about that. Updating INDRAWABLE will automatically mark SYSMEM
outdated.