Remove unreachable code in get_active_blog_for_user()

[jeremyfelt]

get_active_blog_for_user() accounts for a case where get_user_meta( $user_id, 'primary_blog', true ); returns false. I believe the only possible way for this to happen is via a misguided filter on get_user_metadata.

If for some reason false was returned, the existing code sets the user as a subscriber on the first site it finds the user has access to, overwriting any existing capabilities. (See also #15316)

The function then returns a blog object that may not meet the full expectations of a blog object being returned by the function. (See also #18789)

The attached patch removes this extra, unnecessary code.

[SergeyBiryukov]

Related: ​mu:1928, [16179].

[nacin]

I believe the only possible way for this to happen is via a misguided filter on get_user_metadata.

It seems like this could also occur if a user simply doesn't have a primary_blog. This could happen on initial conversion from single-site to multisite, or if user tables are shared, I guess.

[jeremyfelt]

If a user is a member of at least one blog, and has no primary blog assigned, then this could be reached.

I haven't tested how to trigger that scenario, but the code itself appears harmless either way.