oggdemux: fix unknown duration playing Ogg over HTTP

If the duration is not known from the chain, it might be known
by the startup seek.

This fixes failure to seek.

Merged with a patch from Tim-Philipp Müller <tim@centricular.com>

https://bugzilla.gnome.org/show_bug.cgi?id=768991

ext/ogg/gstoggdemux.c

@@ -344,7 +344,9 @@ gst_ogg_pad_src_query (GstPad * pad, GstObject * parent, GstQuery * query)
               else
                 stop = MAX (idx_time, stop);
             } else {
-              stop = -1;        /* we've no clue, sadly, without seeking */
+              stop = ogg->push_time_length;
+              if (stop == -1)
+                stop = ogg->total_time;
             }
           }
         }