fix(views): allows passing base_url through gallery view

Although the pagination view choses a sensible value for base_url, devs could
pass in base_url to elgg_list_entities() for lists, but not galleries. This
remedies this inconsistency.

Fixes #7669
Merge pull request #7672 from mrclay/7669_base_url

fix(views): allows passing base_url through gallery view