vc1parse: unref caps when it is empty in renegotiate()

https://bugzilla.gnome.org/show_bug.cgi?id=737724
diff --git a/gst/videoparsers/gstvc1parse.c b/gst/videoparsers/gstvc1parse.c
index c2235ce..39fd6d0 100644
--- a/gst/videoparsers/gstvc1parse.c
+++ b/gst/videoparsers/gstvc1parse.c
@@ -345,6 +345,7 @@
     }
   } else if (gst_caps_is_empty (allowed_caps)) {
     GST_ERROR_OBJECT (vc1parse, "Empty caps");
+    gst_caps_unref (allowed_caps);
     return FALSE;
   } else {
     GST_DEBUG_OBJECT (vc1parse, "Using input header/stream format");