Merge change 4526 into donut

* changes:
  Log null author command in authordriver.cpp (bug 1922537) Note this does not resolve the root cause for the mediaserver crash reported in bug 1922537: 1. why was a null author command received from the author engine (PV is looking into this issue)? 2. why was the time stamp out of the order (QCOM and PV are looking into this issue)? 3. why did we receive multiple event callbacks for a single state transition request (QCOM is looking into this issue)?

android/author/authordriver.cpp

@@ -1100,7 +1100,11 @@ void AuthorDriver::CommandCompleted(const PVCmdResponse& aResponse)
 {
     author_command *ac = (author_command *)aResponse.GetContext();
     status_t s = aResponse.GetCmdStatus();
-    LOGV("Command (%d) completed with status(%d)", ac->which, s);
+    LOGV("Command (%d) completed with status(%d)", ac? ac->which: -1, s);
+    if (ac == NULL) {
+        LOGE("CommandCompleted: Error - null author command!");
+        return;
+    }
 
     if (ac->which == AUTHOR_SET_OUTPUT_FORMAT) {
         mSelectedComposer = aResponse.GetResponseData();