Fix the computation of min/max of images with a finite nodata.

[joa-quim]

Fix some cases of: I -/+ const

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.41379% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.07%. Comparing base (69d5c67) to head (a0dc606).

Files with missing lines	Patch %	Lines
src/grd_operations.jl	72.72%	6 Missing ⚠️
src/gdal_utils.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1865      +/-   ##
==========================================
+ Coverage   86.03%   86.07%   +0.03%     
==========================================
  Files         177      177              
  Lines       26529    26549      +20     
==========================================
+ Hits        22825    22852      +27     
+ Misses       3704     3697       -7     

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