What does this implement/fix? Explain your changes.

User can add arbitrary strings to sys.path. When we probe for assemblies in sys.path the ones that were not valid paths caused the probing to fail, never reaching the valid ones that actually had the desired assembly.

This change handles these cases by generating a warning and continuing to probe in other directories.

Does this close any currently open issues?

fixes #2376

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Updated the CHANGELOG