[CX] Enforce IFrameWriter protocol

Currently, IFrameWriter protocol says that nextFrame() and flush() should never be called on a frame that has failed. in addition, the protocol says that once a failure occur somewhere in the pipeline, all operators in the pipeline should be notified of a failure().

Currently, there are some operators that don't enforce this strictly. Enforcement of the protocol should be done in a central location to ensure proper detection of bad behaving operators and allow early fixes of such obscure bugs.