Check node type before getOwner() call

[alecpl]

Fixes #1345

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.21%. Comparing base (ed901a9) to head (6313e8d).
⚠️ Report is 46 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/CalDAV/Schedule/Plugin.php	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1614      +/-   ##
============================================
- Coverage     97.23%   97.21%   -0.03%     
- Complexity     2836     2838       +2     
============================================
  Files           175      175              
  Lines          9028     8854     -174     
============================================
- Hits           8778     8607     -171     
+ Misses          250      247       -3     

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[ChristophWurst]

Looks good! Thanks

[ChristophWurst]

Coverage dropped a bit. A test case in tests/Sabre/CalDAV/Schedule/PluginBasicTest.php should help.

[alecpl]

I'm not sure how to reproduce or add a test for this case. So, someone else would have to do this.