Fix the dataid sorting

[mraspaud]

When the query and the dataids to be sorted have a different set of keys, the sorting would sometimes not go through all the keys before returning. We fix this by converting a spurious break into a continue. This fixes #1549.

• Closes Satpy problems with MODIS #1549
• Tests added

[codecov]

Codecov Report

Merging #1556 (143304c) into master (f863bc2) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1556      +/-   ##
==========================================
+ Coverage   92.15%   92.18%   +0.02%     
==========================================
  Files         251      251              
  Lines       36764    36777      +13     
==========================================
+ Hits        33881    33902      +21     
+ Misses       2883     2875       -8     

Flag	Coverage Δ
behaviourtests	4.49% <0.00%> (-0.01%)	⬇️
unittests	92.71% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
satpy/dataset/dataid.py	94.05% <100.00%> (ø)
satpy/tests/test_dataset.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_vii_base_nc.py	98.73% <0.00%> (+1.26%)	⬆️
satpy/tests/reader_tests/test_nwcsaf_msg.py	98.31% <0.00%> (+1.68%)	⬆️
satpy/tests/reader_tests/test_vii_l1b_nc.py	100.00% <0.00%> (+2.81%)	⬆️
satpy/tests/reader_tests/test_vii_l2_nc.py	100.00% <0.00%> (+6.06%)	⬆️

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[djhoese]

LGTM just to make sure, there is a break a couple lines below your change, does this need to change?

[mraspaud]

The one after is fine, as the distance becomes infinite, there is no point in continuing.