the editor, faster on phones

two fixes for the editor on a phone, both from feedback.

• –looks respond straight away: after every tap on a look, the phone redrew every tile in the looks strip, 17 of them film stocks graded on its processor. that held up the screen for a second or two, long enough for a tap to seem not to land. the tiles now redraw only when your own adjustments change.
• –no more crashes on some phones: a few phones say they can run the editor's high-precision mode and then refuse it, which took the editor down. those phones now get the standard precision any simple grade already uses, and the editor keeps going.