Bug: Searching for an aliased tag returns an empty page instead of
showing the results for the real tag.
Cause: The query parsing code runs the search string through
`.mb_chars.downcase` before calling `TagAlias.to_aliased`, so the input
to `to_aliased` is actually a ActiveSupport::Multibyte::Chars object.
This breaks the `aliases[name]` hash lookup because `name` is not a
plain string.
Fixup for c7bcce429.
b50b7f2a91