Fix infinite coordinates failing to be equal

[mraspaud]

The equality between two infinite coordinates was removed in 5079259 through the unwrapping of the longitude returning a NaN instead of Inf in that case. This PR restores the previous behaviour.

• Tests added
• Tests passed

Example of failing script:

    from satpy import Scene
    from glob import glob
    import os
    from satpy.utils import debug_on
    debug_on()
    datadir = "/home/a001673/data/satellite/Meteosat-11/seviri/lvl1.5/2018/02/28/HRIT"

    scn = Scene(filenames=glob(os.path.join(datadir, "*")),
                reader='seviri_l1b_hrit',
                )
    composite = "overview"
    scn.load([composite])
    newscn = scn.resample("moll")
    newscn.save_datasets(base_dir='/tmp', tiled=True, blockxsize=512, blockysize=512, driver='COG', overviews=[])

[codecov]

Codecov Report

Merging #441 (764da79) into main (119f9ad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #441   +/-   ##
=======================================
  Coverage   94.24%   94.24%           
=======================================
  Files          68       68           
  Lines       12294    12300    +6     
=======================================
+ Hits        11586    11592    +6     
  Misses        708      708           

Flag	Coverage Δ
unittests	94.24% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pyresample/spherical.py	98.21% <100.00%> (+0.01%)	⬆️
pyresample/test/test_spherical.py	100.00% <100.00%> (ø)

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[coveralls]

Coverage increased (+0.003%) to 94.089% when pulling 764da79 on mraspaud:fix-unwrap-scoord into 119f9ad on pytroll:main.

[djhoese]

I'm guessing this logic shouldn't be part of unwrap_radians for some reason? I'm OK with that, but just want to make sure. Feel free to merge.