Fix apiurl_aliases handling in OscOptions.__getitem__

[dmach]

Fixes: #1439

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a2e7383) 30.74% compared to head (c790134) 30.75%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1440   +/-   ##
=======================================
  Coverage   30.74%   30.75%           
=======================================
  Files          49       49           
  Lines       17740    17742    +2     
=======================================
+ Hits         5455     5457    +2     
  Misses      12285    12285           

Files	Coverage Δ
osc/__init__.py	100.00% <100.00%> (ø)
osc/commandline.py	19.08% <0.00%> (ø)
osc/conf.py	54.67% <80.00%> (+0.13%)	⬆️

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[pallaswept]

Tested this and it fixes the issue for me. For reference: #1439 (comment)

Thanks @dmach !