FIX: [gles] fix karaoke and teletext rendering

This is a partial revert of 144f7352fe0dc4145161056aef9986a6db81dace

It fixes karaoke and teletext on gles.
I don't know what was the original issue if subtitles, but they seem still fine. Actually, I don't think this is used (anymore?) for subtitles.

/cc @davilla @t-nelson