videoaggregator: Fix locking around vagg->info
Take GST_OBJECT_LOCK when writing vagg->info, so that reading in
subclasses is protected against races, as documented in the struct.
/*< public >*/
/* read-only, with OBJECT_LOCK */
GstVideoInfo info;gst_video_aggregator_default_negotiated_src_caps should take the
GST_VIDEO_AGGREGATOR_LOCK to avoid racing with
gst_video_aggregator_reset called by
gst_video_aggregator_release_pad of the last sinkpad. Otherwise it can
happen that latency = gst_util_uint64_scale (... gets called with a
zero framerate.
There doesn't seem to be any reason not to use the local info instead
of vagg->info, so do that.