Check if we are dividing by zero when rescaling

[darbyjohnston]

Add a check to make sure we are not dividing by zero when rescaling.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.50%. Comparing base (c51d995) to head (b38f801).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2016   +/-   ##
=======================================
  Coverage   84.50%   84.50%           
=======================================
  Files         181      181           
  Lines       13223    13225    +2     
  Branches     1202     1202           
=======================================
+ Hits        11174    11176    +2     
  Misses       1866     1866           
  Partials      183      183           

Flag	Coverage Δ
py-unittests	84.50% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/opentime/rationalTime.h	95.91% <100.00%> (+0.08%)	⬆️

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