VoD: fix deadlock between RTSP and VLM

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>

modules/stream_out/rtsp.c

@@ -1052,16 +1052,17 @@ static int RtspHandler( rtsp_stream_t *rtsp, rtsp_stream_id_t *id,
                     info[infolen - 2] = '\0'; /* remove trailing ", " */
                     httpd_MsgAdd( answer, "RTP-Info", "%s", info );
                 }
+            }
+            vlc_mutex_unlock( &rtsp->lock );
+
+            if (ses != NULL)
+            {
                 if (vod)
                 {
                     vod_play(rtsp->vod_media, psz_session, &start, end);
                     npt = start;
                 }
-            }
-            vlc_mutex_unlock( &rtsp->lock );
 
-            if (ses != NULL)
-            {
                 double f_npt = (double) npt / CLOCK_FREQ;
                 httpd_MsgAdd( answer, "Range", "npt=%f-", f_npt );
             }
@@ -1089,15 +1090,7 @@ static int RtspHandler( rtsp_stream_t *rtsp, rtsp_stream_id_t *id,
             ses = RtspClientGet( rtsp, psz_session );
             if (ses != NULL)
             {
-                if (id == NULL)
-                {
-                    assert(vod);
-                    int64_t npt;
-                    vod_pause(rtsp->vod_media, psz_session, &npt);
-                    double f_npt = (double) npt / CLOCK_FREQ;
-                    httpd_MsgAdd( answer, "Range", "npt=%f-", f_npt );
-                }
-                else /* "Mute" the selected track */
+                if (id != NULL) /* "Mute" the selected track */
                 {
                     bool found = false;
                     for (int i = 0; i < ses->trackc; i++)
@@ -1123,6 +1116,15 @@ static int RtspHandler( rtsp_stream_t *rtsp, rtsp_stream_id_t *id,
                 RtspClientAlive(ses);
             }
             vlc_mutex_unlock( &rtsp->lock );
+
+            if (ses != NULL && id == NULL)
+            {
+                assert(vod);
+                int64_t npt = 0;
+                vod_pause(rtsp->vod_media, psz_session, &npt);
+                double f_npt = (double) npt / CLOCK_FREQ;
+                httpd_MsgAdd( answer, "Range", "npt=%f-", f_npt );
+            }
             break;
         }