Only generate new uuid if not already a valid one

[francescalb]

Description:

When asking to sync_attributes with the uuid name_policy the name is regenerated for all, even if the alrealy have a valid name within this name_policy. This makes it impossible to add to an already existing ontology.

Type of change:

• Bug fix.
• New feature.
• Documentation update.

Checklist:

This checklist can be used as a help for the reviewer.

• Is the code easy to read and understand?
• Are comments for humans to read, not computers to disregard?
• Does a new feature has an accompanying new test (in the CI or unit testing schemes)?
• Has the documentation been updated as necessary?
• Does this close the issue?
• Is the change limited to the issue?
• Are errors handled for all outcomes?
• Does the new feature provide new restrictions on dependencies, and if so is this documented?

Comments:

[codecov-commenter]

Codecov Report

Merging #526 (591511b) into master (dd7ea07) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
+ Coverage   65.46%   65.49%   +0.03%     
==========================================
  Files          16       16              
  Lines        3081     3084       +3     
==========================================
+ Hits         2017     2020       +3     
  Misses       1064     1064              

Impacted Files	Coverage Δ
ontopy/ontology.py	70.03% <100.00%> (+0.13%)	⬆️

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[jesper-friis]

I will suggest to check that obj.name starts with name_prefix. Except for that I think this is the right fix.

I approve to not cause unnecessarily delays.