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!".
#require test-repo pyflakes
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate 'set:**.py or grep("^!#.*python")' 2>/dev/null \
> | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
tests/filterpyflakes.py:61: undefined name 'undefinedname'