Fix crash in Package.info() when working with a git package, raise an exception as expected

[dmach]

Fixes: #2123

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.94%. Comparing base (db7e182) to head (8121ff7).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
osc/obs_scm/package.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2125   +/-   ##
=======================================
  Coverage   33.93%   33.94%           
=======================================
  Files         199      199           
  Lines       27030    27025    -5     
=======================================
  Hits         9173     9173           
+ Misses      17857    17852    -5     

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