Include provider tag in complete attribution tag list

Ensure that the list of attribution tags considered "producer" or "source"
includes the attribution tag of the location provider itself. This is
particularily important if the location provider does not use any
attribution tags, as this ensures the null tag is included in the list.

Bug: 186572461
Test: manual
Change-Id: I9a7b2e9b67cbeb700d5c04730541ad4bf051d0da