libgui: Always allow allocation on connect

This change places BufferQueue into a predictable state where
allocation is allowed whenever a producer connects. This allows clients
to disconnect and reconnect without having to worry about being locked
out of allocation.

Bug: 20554276
Change-Id: Ic0f920a3d4204f2cafdfa69e46f3bb4204571d7e

libs/gui/BufferQueueProducer.cpp

@@ -871,6 +871,7 @@ status_t BufferQueueProducer::connect(const sp<IProducerListener>& listener,
     mCore->mBufferHasBeenQueued = false;
     mCore->mDequeueBufferCannotBlock =
             mCore->mConsumerControlledByApp && producerControlledByApp;
+    mCore->mAllowAllocation = true;
 
     return status;
 }