Make gm_get_motion_vector respect allow_high_precision_mv

This fixes a rare encode/decode mismatch due to inconsistent
rounding of NEARMV/NEARESTMV vs. ZEROMV motion vectors when both
global motion and ref-mv are enabled.

Change-Id: Ia2bbaf63020f5ce7762e027f9bf835fd96797bec
4 files changed