1. m_writerQueue is now shared by recorder control and asset writer
to ensure it lives long enough.
2. m_delegate->method() calls from async block can be dangerous, since by the time
this block is actually executed, delegate can be deleted already. This fix uses
Q_INVOKABLE and invokeMethod with QueuedConnection instead.
3. -finishWritingWithCompletionHandler: is async and when the block finally gets
executed, lock and 'if aborted' test are still needed.
4. Simplify the logic and reduce locking.
Change-Id: If23daf2fe22043244033427a7f6517a0fe3f23d1
Reviewed-by: Yoann Lopes <yoann.lopes@qt.io>
f97e1988a6