Modify profile viewer so that when in 'Sum' mode, parts of profiles with no valid values are NaN rather than zero

[astrofrog]

No description provided.

[codecov]

Codecov Report

Merging #2298 (acc1f92) into main (1c71837) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2298      +/-   ##
==========================================
+ Coverage   88.15%   88.17%   +0.02%     
==========================================
  Files         247      247              
  Lines       23316    23325       +9     
==========================================
+ Hits        20554    20567      +13     
+ Misses       2762     2758       -4     

Impacted Files	Coverage Δ
glue/utils/array.py	88.49% <100.00%> (+0.42%)	⬆️
glue/conftest.py	67.85% <0.00%> (+4.76%)	⬆️

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[pllim]

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