Add --prevent-empty-failure flag

[vzqzac]

This flag aims to prevent a failure throw when there are no files that
match either the given glob or the default one, this can be helpful in
some cases such as some pre-commit hooks that run against the diff-ed
files, for example:

Commiting files that do not include any erb extension, then, running
linters as part of a pre-commit check, including (as an example) rubocop,
reek, stylelint, fasterer, and erb-lint, would throw an error since there are no
files to run erb-lint against, preventing the user to properly create a
commit.

Note: The flag name might not be the most suitable, open to discuss a better one 😄