Update vulnerability_map.py

[tmorganbrown]

I'm not sure if this reverted or I never tired the fix, but it doesn't work with my risk maps unless I calculate the max directly with numpy.

[YaoTingYao]

Check if max_value is None to optimize processing for rasters with metadata without loading the entire array, and calculate max_value for rasters without metadata.

max_value = in_band.GetMaximum()
if max_value is None:
    # Calculate max_value for rasters without metadata
    max_value = np.max(arr)

[YaoTingYao]

Hi @tmorganbrown, I've made change requests in the previous PR. This change would check if max_value is None to optimize processing for rasters with metadata without loading the entire array, and calculate max_value for rasters without metadata.

Please commit these changes to your branch so I can merge the PR. Alternatively, I can merge the PR first and make the changes afterward. Please let me know your preference. Thx!

[YaoTingYao]

Hi @tmorganbrown, I will merge the PR firstly and make the changes afterward. Thanks again for your feedback and contribution. Cheers!