ART: cleanup exit_block_ in graph if exit block is removed

If we remove the exit block from the graph (for example method
contains infinite loop) we should also clean the field exit_block_
in graph. At least inliner expects it.

Change-Id: Icda668da2233cdd6cd673635a1949f5ed34cf270
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 0e0b83e..77ded29 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -127,6 +127,9 @@
       // Remove the block from the list of blocks, so that further analyses
       // never see it.
       blocks_[i] = nullptr;
+      if (block->IsExitBlock()) {
+        SetExitBlock(nullptr);
+      }
     }
   }
 }
@@ -1870,7 +1873,7 @@
   DCHECK(block->GetPhis().IsEmpty());
 
   if (block->IsExitBlock()) {
-    exit_block_ = nullptr;
+    SetExitBlock(nullptr);
   }
 
   RemoveElement(reverse_post_order_, block);