fix guessVocabularyFromURI when some vocabulary has no URI space (Skosmos 3)

[osma]

Reasons for creating this PR

Same as PR #1559 but for Skosmos 3.

Link to relevant issue(s), if any

• Follow-up fix to Don't crash on incomplete vocabulary configuration #1409 which made it possible to omit URI space from vocabulary configuration

Description of the changes in this PR

When constructing a cache of URI space to vocabulary mappings, don't include vocabularies that don't have a URI space.

Known problems or uncertainties in this PR

Ideally there should be a unit test, but we don't have any existing tests for empty URI space either.

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e5db224) 70.53% compared to head (3c4fae6) 70.54%.

Additional details and impacted files

@@               Coverage Diff               @@
##             skosmos-3    #1560      +/-   ##
===============================================
+ Coverage        70.53%   70.54%   +0.01%     
- Complexity        1643     1644       +1     
===============================================
  Files               32       32              
  Lines             4313     4315       +2     
===============================================
+ Hits              3042     3044       +2     
  Misses            1271     1271              

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