fix(ModflowUzf1): fix for loading negative iuzfopt

[jlarsen-usgs]

Closes #1406

[codecov]

Codecov Report

Merging #1408 (095b455) into develop (53734e5) will decrease coverage by 44.789%.
The diff coverage is 0.000%.

@@              Coverage Diff               @@
##           develop     #1408        +/-   ##
==============================================
- Coverage   74.829%   30.040%   -44.790%     
==============================================
  Files          249       249                
  Lines        53563     52123      -1440     
==============================================
- Hits         40081     15658     -24423     
- Misses       13482     36465     +22983     

Impacted Files	Coverage Δ
flopy/modflow/mfuzf1.py	7.031% <0.000%> (-80.242%)	⬇️
flopy/mf6/utils/testutils.py	0.000% <0.000%> (-93.334%)	⬇️
flopy/mfusg/mfusgsms.py	6.190% <0.000%> (-91.474%)	⬇️
flopy/mf6/utils/postprocessing.py	9.259% <0.000%> (-88.889%)	⬇️
flopy/modflow/mfevt.py	7.812% <0.000%> (-87.007%)	⬇️
flopy/mf6/utils/lakpak_utils.py	2.097% <0.000%> (-85.315%)	⬇️
flopy/modflow/mfhyd.py	13.223% <0.000%> (-85.124%)	⬇️
flopy/utils/swroutputfile.py	10.714% <0.000%> (-85.079%)	⬇️
flopy/utils/mtlistfile.py	4.620% <0.000%> (-84.700%)	⬇️
flopy/modflowlgr/mflgr.py	6.271% <0.000%> (-84.354%)	⬇️
... and 205 more