BUGFIX: Initialize isolist for ellipse fitting

[tepickering]

when the ellipse fitting failed, isolist wasn't initialized which caused an uncaught exception:

"/mmt/condaforge/envs/mmtwfs/lib/python3.13/site-packages/mmtwfs/wfs.py", line 1304, in measure_slopes vlt_seeing, raw_vlt_seeing = self.vlt_seeing( ~~~~~~~~~~~~~~~^ slope_results["coadded_spot"], mode=mode, airmass=airmass ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ) ^ File "/mmt/condaforge/envs/mmtwfs/lib/python3.13/site-packages/mmtwfs/wfs.py", line 1045, in vlt_seeing if len(isolist) > 0: ^^^^^^^ UnboundLocalError: cannot access local variable 'isolist' where it is not associated with a value

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.00%. Comparing base (b466034) to head (5da5271).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #56   +/-   ##
=======================================
  Coverage   85.00%   85.00%           
=======================================
  Files          10       10           
  Lines        2327     2328    +1     
=======================================
+ Hits         1978     1979    +1     
  Misses        349      349           

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