bufferqueue: workaround: allow NULL fence with queueBuffer (DO NOT MERGE)

On one device there is a bug, not yet root-caused, that causes fence
fds to not make it across binder from producer to consumer in the
IGraphicBufferProducer::queueBuffer call. Rather than returning an
error, which the producer typically treats as a fatal error, this
change allows the buffer to be queued with no fence. This avoids an
application crash at the risk of (likely single-frame) visible
corruption.

Bug: 17946343
Change-Id: I9ca89f94098c455e1e90f5f58d5336c936b04a9c