ffserver: free AVStream st before wiping context

Should fix FFmpeg Coverity Scan issue #732269

Signed-off-by: Reynaldo H. Verdejo Pinochet <r.verdejo@sisa.samsung.com>

ffserver.c

@@ -3468,6 +3468,7 @@ static int rtp_new_av_stream(HTTPContext *c,
     fail:
         if (h)
             ffurl_close(h);
+        av_free(st);
         av_free(ctx);
         return -1;
     }