
When source frame is altref, we only do zero-mv mode, so we can skip the find_predictors(). No change in compression. Small speed gain, ~1%. Only affects 1 pass vbr with lookhead altref, for ytlive with the macro flag USE_ALTREF_FOR_ONE_PASS on. Change-Id: I9318c5da8521f017bf54919cd652438b3a6313d1