The test for pts==0 results in every subtitle in the overlay container being rendered at start of file.
#2565 results in every subitle from an external file being loaded into the overlay container at start of file.
This results in hundreds of subtitles being rendered which is slow and ugly. See:
Remove this test.
Also remove setting the media_pts to the predicted media_pts as that causes a subtitle flurry after seeking while GPU fifo fills