Subtitles: Hint about off-center HAlign values

[wolfgangw]

Off-center HAlign values may be intentional - we've seen works with "left"/"right" throughout all titles and occasionally a title with fine-tuned positioning wrt crowded images. It is rare, though.

See "Nran Guyne / Sajat Nova" reel 2 (subtitle reel 1) for an example of unintentional "left" - a couple in the opening credits, two in the film's opening reel - where the render will end up exceeding image border.

A hint for off-center values plus calculation where the subtitle would end up at should be useful.