Frame zero in saturation correction - Roman does not have zero frame

[nden]

This is a follow-up on #81 - adds a guard for "frame zero" , since Roman does not have one.

[codecov]

Codecov Report

Merging #89 (3f39c1d) into main (6f2dba7) will increase coverage by 18.46%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main      #89       +/-   ##
===========================================
+ Coverage   71.66%   90.13%   +18.46%     
===========================================
  Files          16       16               
  Lines        2432     2433        +1     
===========================================
+ Hits         1743     2193      +450     
+ Misses        689      240      -449     

Impacted Files	Coverage Δ
src/stcal/ramp_fitting/ramp_fit.py	96.66% <100.00%> (+44.98%)	⬆️
src/stcal/ramp_fitting/gls_fit.py	63.36% <0.00%> (+2.22%)	⬆️
src/stcal/dark_current/dark_sub.py	84.42% <0.00%> (+2.45%)	⬆️
src/stcal/ramp_fitting/utils.py	98.50% <0.00%> (+17.91%)	⬆️
src/stcal/ramp_fitting/ols_fit.py	93.90% <0.00%> (+21.11%)	⬆️
src/stcal/jump/twopoint_difference.py	99.17% <0.00%> (+21.48%)	⬆️
src/stcal/dark_current/dark_class.py	100.00% <0.00%> (+30.95%)	⬆️
src/stcal/jump/constants.py	100.00% <0.00%> (+71.42%)	⬆️
src/stcal/dynamicdq.py	100.00% <0.00%> (+72.72%)	⬆️
... and 1 more

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[nden]

This is ready

[hbushouse]

Looks good. Don't forget the change log!

[ddavis-stsci]

I am able to run ramp fit on Roman data with this change!