paths: use single loop for both search=None|pattern cases
This will help porting to the formatter API. This patch adds test for empty
pathitems to make sure "hg paths" never say "not found!".
paths: reorder else clause for readability of subsequent patches
This prepares for porting to the formatter API. Future patches will use a
single loop to handle both search=None|pattern cases because formatter output
should be the same. "pathitems" will be switched instead.