Fix bug 3385881

Launch signals and threads are not always
matched in index.  Threads grab launch indexes
as they start which may not be the order in which
they were launched.

Change-Id: I1ff42c3df5d7ebb46de6329ebd11ef67a5fc58ca

libs/rs/rsContext.cpp

@@ -735,6 +735,8 @@ Context::~Context() {
     mWorkers.mRunningCount = (int)mWorkers.mCount;
     for (uint32_t ct = 0; ct < mWorkers.mCount; ct++) {
         mWorkers.mLaunchSignals[ct].set();
+    }
+    for (uint32_t ct = 0; ct < mWorkers.mCount; ct++) {
         int status = pthread_join(mWorkers.mThreadId[ct], &res);
     }
     rsAssert(!mWorkers.mRunningCount);