find_event_pipeline/find_event handling of "complex cadence" is broken

[texadactyl]

Describe the bug

The find_event_pipeline / find_event handling of a "complex cadence" is broken and may have never worked.

To Reproduce

Steps to reproduce the behavior:

1. Write a program which calls find_event_pipeline using the on_source_complex_cadence parameter.
2. Execute it.
3. See error:

  File "/usr/local/lib/python3.8/dist-packages/turbo_seti-2.0.8.1-py3.8.egg/turbo_seti/find_event/find_event.py", line 450, in find_events
    for i in range(1, number_of_ons + 1):

UnboundLocalError: local variable 'number_of_ons' referenced before assignment

It's true! The variable number_of_ons is never computed in a complex cadence situation.

Expected behavior

I expect the complex cadence feature to work. Certainly, it should not crash.

Setup

• Python version: 3.8.5
• turbo_seti version: 2.0.8.1
• blimpy version: 2.0.5