TST: skip tests needing xlrd
Merge pull request #3517 from lodagro/test_excel

TST: skip tests needing xlrd
Fixed Unbound Variable `edge` access when BinGrouper is empty

Incorrectly accessed variable `edge` instead of pre-filled value `start`.

Signed-off-by: Kevin Stone <kevinastone@gmail.com>
Merge branch 'PR3510'

* PR3510:
  Fixed Unbound Variable `edge` access when BinGrouper is empty