Bundled Themes: Consistently check for `WP_Error` before outputting `get_the_tag_list()`.

Some themes already had these checks in place as a result of [41756], but not others.

Props sixhours, davidakennedy, SergeyBiryukov.
Fixes #39860.
Built from https://develop.svn.wordpress.org/trunk@47886


git-svn-id: https://core.svn.wordpress.org/trunk@47660 1a063a9b-81f0-0310-95a4-ce76da25c4cd