Update zm_stream.cpp

--- ZoneMinder-master/src/zm_stream.cpp	Wed Sep 18 06:00:06 2013 UTC
+++ ZoneMinder-master.rtsp/src/zm_stream.cpp	Tue Sep 24 12:05:59 2013 UTC
@@ -27,6 +27,13 @@
 
 StreamBase::~StreamBase()
 {
+#if HAVE_LIBAVCODEC
+    if ( vid_stream )
+    {
+	delete vid_stream;
+	vid_stream = NULL;
+    }
+#endif
     closeComms();
 }