build_arg_list: Raise an exception if an invalid output file name is given

[seisman]

Description of proposed changes

When working on PR #3334, I realized that we didn't check if the outfile parameter passed to build_arg_list is valid or not. Some invalid values are "", ".", ".." or a string ending with / or \.

This PR enhances the build_arg_list function to check if the outfile argument is valid. We can't check all cases but at least we can raise an exception for a few common cases.

This PR will further simplify #3334.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code

[weiji14]

Looks ok I think, just one suggestion to check the Windows-style folders ending with \\.

[seisman]

/format