ENH: Allow the .xyz parser to handle empty lines

[BvB93]

cc @maxsw2

Ensure that .xyz files with empty lines, such as the one below, are considered valid.

2
Frame 1
H 1.0 0.0 0.0
H 0.0 0.0 0.0

2
Frame 2
H 2.0 0.0 0.0
H 1.0 0.0 0.0

[codecov]

Codecov Report

Merging #277 (3af6648) into master (11ad965) will decrease coverage by 0.03%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #277      +/-   ##
==========================================
- Coverage   75.32%   75.29%   -0.04%     
==========================================
  Files          66       66              
  Lines        7093     7076      -17     
  Branches     1358     1355       -3     
==========================================
- Hits         5343     5328      -15     
  Misses       1410     1410              
+ Partials      340      338       -2     

Impacted Files	Coverage Δ
FOX/io/read_xyz.py	71.15% <57.14%> (+0.13%)	⬆️
FOX/armc/armc_pt.py	85.12% <0.00%> (-2.48%)	⬇️

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