The deadlock would occur when the VLM would stop an instance and detach
its RTP output, at the same time as an RTSP client would issue a VoD
command to the VLM.

Unfortunately this introduces a race condition where wrong RTP-Info can
be returned.
(cherry picked from commit 7ac6ae55e2496c7178ce0b15a3c16a2db464a38c)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>