Original commit message from CVS:
Patch by: Rene Stadler <mail at renestadler de>
* gst/gsttagsetter.c: (gst_tag_setter_merge_tags):
Merging an empty list with another list in KEEP_ALL mode should
yield an empty list as result and not the second list (#512578).
* tests/check/gst/gsttagsetter.c:
Add unit test for tag merge modes and the aforementioned bug.