stash push -u: don't create empty stash

When introducing the stash push feature, and thus allowing users to pass in a pathspec to limit the files that would get stashed in df6bba0937 ("stash: teach 'push' (and 'create_stash') to honor pathspec", 2017-02-28), this developer missed one place where the pathspec should be passed in. Namely in the call to the 'untracked_files()' function in the 'no_changes()' function. This resulted in 'git stash push -u -- <non-existant>' creating an empty stash when there are untracked files in the repository other that don't match the pathspec. As 'git stash' never creates empty stashes, this behaviour is wrong and confusing for users. Instead it should just show a message "No local changes to save", and not create a stash. Luckily the 'untracked_files()' function already correctly respects pathspecs that are passed to it, so the fix is simply to pass the pathspec along to the function. Reported-by: Marc Strapetz <marc.strapetz@syntevo.com> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>