www_listing: avoid unnecessary work for common cases

www_listing: avoid unnecessary work for common cases

We need to branch for non-empty `q=' parameters anyways, but
`q=' is usually empty/unset.  While we're in the area, `chomp'
reads `$/' while `chop' is simpler.  Furthermore, we can shave
a few bytes off the form HTML by omitting spaces before `/>'
and placing `\n' to wrap long lines before attribute names.