Quick compiler: fix DCHECK

Cherry-pick from internal 532582

A DCHECK intended to verify the soundness of the mapping between
a wide Dalvik value and a pair of temp registers incorrectly fired
when the temp register pair was associated with a wide temporary
(i.e. - when (SReg() == INVALID_SREG)).

In this particular situation, the wideness flag is meaningful only when
there is an associated valid vreg.  Code rearranged to only perform
the DCHECK and reset the partner's wideness bit when we're dealing with
a live wide value.

b/16484538

Change-Id: I3b8a7bebc5d918c65ea56ae8db0a8a5cd8003386