Post Formats: Allow to check for any post format

[obenland]

It would be great if themes could check if any post format has been assigned to a post. This would make it especially easy to check if no post format has been assigned, something that is hard to do in has_post_format's current setup.

With the change in r24934 it is only a matter of making the passed format argument optional and checking for it.

[DrewAPicture]

+1 for this. @obenland: Looks like you missed marking $format (optional) in the docblock.

We need to update the short description anyway following [24934] since it can (currently) be one or many.

[nacin]

The use of ! empty( $single ) felt like a code smell — under what circumstances would an item in this array be empty? It seems like that could occur if someone passed false, null, etc., as $format, which would then get converted to array( 0 => false ).

24906.3.diff​ tries a different branching of the logic.

[duck_]

In 26350:

Allow has_post_format() to be used to check for any format.

Calling has_post_format() with an empty list of $format will check if the
provided post has any associated format at all.

Props obenland, DrewAPicture, nacin. Fixes #24906.