Show option-based errors before unexpected positional errors

[natecook1000]

This pushes any errors indicated by unexpected arguments after parsing out to the same late position. We were previously stopping immediately when the command is a leaf node; that isn't necessary and created an awkward second error path.

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[natecook1000]

@swift-ci Please test