init: do not handle control messages after shutdown

We already stop queue'ing new control messages, but we forgot to stop
handling those control messages that are already queued.  This CL
fixes that.

Bug: 150863651
Test: CF reboots appropriately
Merged-In: Ifea07a30b868de23eb735db10d8bae410e1b98bb
Change-Id: Ifea07a30b868de23eb735db10d8bae410e1b98bb
(cherry picked from commit 22d6348845)

init/init.cpp

@@ -879,7 +879,9 @@ int SecondStageMain(int argc, char** argv) {
                 (*function)();
             }
         }
-        HandleControlMessages();
+        if (!IsShuttingDown()) {
+            HandleControlMessages();
+        }
     }
 
     return 0;