info: fix performance issue with registering categories after gst_init()

info: fix performance issue with registering categories after gst_init()

When registering a new debug category after gst_init(), simply check
the existing patterns against that new category.

No need to iterate over all categories and recheck them all against
the existing patterns.

Also, no need to re-parse the existing pattern string set via GST_DEBUG
and add the same set of match patterns all over again to the existing
list of match patterns every time we register a new debug category.

Combined with iterating all debug categories on a change this would
make adding debug categories after gst_init() very very very slow.