yapf should error out and list targets which are not found

$ yapf 404.py
yapf: Input filenames did not match any python files # good!

$ yapf -i exists.py 404.py
exit code == 0 # bad :(

expected:
$ yapf -i exists.py 404.py
stderr>>"yapf: Input argument did not match any python files: 404.py"
exit code == 3

Start by reproducing the two yapf command examples from the issue and trace the CLI input-validation path for mixed existing and missing filenames. Done means the command reports each unmatched target on stderr and exits with status 3, while the all-missing case continues to report that no Python files matched.

Written by the indexing model from the issue text.