client: free watch context only once
client: free watch context only once

The watch context is freed when the source is destroyed. Avoids
a CRITICAL when we try to unref the context twice.

hsteinhaus/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,Lachann/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,surround-io/gst-rtsp-server,hsteinhaus/gst-rtsp-server