[NORMATIVE] Always check that mvs are in range
[NORMATIVE] Always check that mvs are in range

Move the check of is_mv_valid() so that it's always called at the
end of assign_mv(), instead of only calling it for NEWMV type modes.
This will allow catching any cases where invalid motion vectors
are generated.

This is normative in that it disallows streams which generate "invalid"
motion vectors via a non-NEWMV mechanism (eg, GLOBALMV). But that was
never intended to be allowed anyway.

BUG=aomedia:1959

Change-Id: I77ad1b841a84b1b3de852b7ef0ba42713554c7a6

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