blast: transaction ordering

This patch fixes two issues.

1) When a pending transactions is not found, don't try to use the iterator.
   This fixes a crash that happens when we are in a bad state.
2) When a transaction doesn't have any callbacks, don't try to send
   callbacks.

Bug: 130643588
Test: SurfaceFlinger_test
Change-Id: I6154c31dbf0b958683324c6b45e1a607691b84e8
diff --git a/services/surfaceflinger/TransactionCompletedThread.cpp b/services/surfaceflinger/TransactionCompletedThread.cpp
index 34df606..b1bf4e2 100644
--- a/services/surfaceflinger/TransactionCompletedThread.cpp
+++ b/services/surfaceflinger/TransactionCompletedThread.cpp
@@ -141,12 +141,12 @@
             } else {
                 ALOGW("there are more latched callbacks than there were registered callbacks");
             }
+            if (listener->second.size() == 0) {
+                mPendingTransactions.erase(listener);
+            }
         } else {
             ALOGW("cannot find listener in mPendingTransactions");
         }
-        if (listener->second.size() == 0) {
-            mPendingTransactions.erase(listener);
-        }
 
         status_t err = addCallbackHandle(handle);
         if (err != NO_ERROR) {