screen-cast-stream: Use flag to signal failed recording
PipeWire supports flags to signal a corrupted buffer. We should use the
flag SPA_CHUNK_FLAG_CORRUPTED for chunk->flags
instead of setting
chunk->size = 0
since the size isn't well defined for arbitrary dmabufs
and should be set to 0.
Sadly clients like obs are using a chunk size of 0 to decide if a buffer
should be imported. Thus we should offer both until clients are using
the flag.