handle empty contraction list in PathInfo

[jcmgray]

Description

This simply handles the case when PathInfo is constructed with an empty path (e.g. for the no-op contraction eq="->") with some defaults rather than raising ZeroDivisionError. See https://github.com/jcmgray/quimb/issues/231.

Status

• [x] Ready to go

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.44%. Comparing base (1a984b7) to head (fda68c3). Report is 3 commits behind head on master.

:exclamation: Current head fda68c3 differs from pull request most recent head c1ca004. Consider uploading reports for the commit c1ca004 to get more accurate results

Additional details and impacted files