Add missing null check in monitor install.

Fixes broken OTA.

Change-Id: I3a89e4755dc6b23d214ec542df3d167e788b904d
diff --git a/runtime/monitor.cc b/runtime/monitor.cc
index b1bf84f..aa47bda 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -123,7 +123,7 @@
   // Publish the updated lock word, which may race with other threads.
   bool success = obj_->CasLockWord(lw, fat);
   // Lock profiling.
-  if (success && lock_profiling_threshold_ != 0) {
+  if (success && owner_ != nullptr && lock_profiling_threshold_ != 0) {
     locking_method_ = owner_->GetCurrentMethod(&locking_dex_pc_);
   }
   return success;