ART: A couple of checks were missed in class LockWord

Change-Id: I1fc2d77f78f49741c1316ccc76b02357158dfdbe
diff --git a/runtime/lock_word-inl.h b/runtime/lock_word-inl.h
index 414b3bb..cf6f83c 100644
--- a/runtime/lock_word-inl.h
+++ b/runtime/lock_word-inl.h
@@ -50,6 +50,7 @@
 inline LockWord::LockWord(Monitor* mon)
     : value_(mon->GetMonitorId() | (kStateFat << kStateShift)) {
   DCHECK_EQ(FatLockMonitor(), mon);
+  DCHECK_LE(mon->GetMonitorId(), static_cast<uint32_t>(kMaxMonitorId));
 }
 
 inline int32_t LockWord::GetHashCode() const {