baseparse: avoid tag list spam if upstream provides bitrate tags already

baseparse: avoid tag list spam if upstream provides bitrate tags already

Explicitly keep track again whether upstream tags or parser tags
already contain bitrate information, and only force a tag update
for a bitrate if we are actually going to add the bitrate to the
taglist later. This fixes constant re-sending of the same taglist,
because upstream provided a bitrate already and we didn't add it,
so we didn't save the 'posted' bitrate, which would then in turn
again trigger the 'bitrate has changed too much, update tags'
code path. Fixes tag spam with m4a files for example.

https://bugzilla.gnome.org/show_bug.cgi?id=679768