Check IsReferenceVReg during deopt

Required since the quick GC maps may not agree with the verifier
ones. Without this check we may copy stale object references into
the shadow frame.

(cherry picked from commit f00baf56ef647684888a407dbb6adadd704a2039)

Bug: 20736048
Change-Id: I7783c8a8ee45cf601b08b4c38f1dec7f7d11380c
6 files changed