PR Summary

This closes #10719

line.set_linewidth was being called after line.set_linestyle but set_linestyle needs self._linewidth. In #10719, the user was passing a string, which maybe they shouldn't, but if set_linewidth is called first, it will cast the string....

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way