Skip more iterations in joint_motion_search
Skip more iterations in joint_motion_search

This CL is an improvement of CL67781.
Skip iterations when the start point of motion
search is unchanged. In CL67781, we break out
when two sub-pixel mvs are both unchanged.
In this CL, we extend the condition to check the
integer mv of search ref frame is unchanged,
while the other ref frame's sub-pixel mv is
unchanged.

For encoder, about 0.25% faster shows by encoding 20 frame
of BasketballDrill_832x480_50.y4m target 800kbps, and
the coding performance changes are neutral.
( 278874 ms -> 278186 ms)

STATS_CHANGED expected

Change-Id: I33ce8d3bea1bb3a06adbebda7b410e3ac1fdc31a

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom