Fix syncing of mixed TV libraries

[sonofsky2010]

If the library was mixed, it can not be found since the it's ID has prefix "Mixed:".

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

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

Comparison is base (a112613) 21.05% compared to head (5b45d52) 21.06%.
Report is 66 commits behind head on master.

Files	Patch %	Lines
jellyfin_kodi/helper/utils.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #774      +/-   ##
==========================================
+ Coverage   21.05%   21.06%   +0.01%     
==========================================
  Files          63       63              
  Lines        8544     8543       -1     
  Branches     1573     1573              
==========================================
+ Hits         1799     1800       +1     
+ Misses       6729     6727       -2     
  Partials       16       16              

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[oddstr13]

I'll eventually get around to testing these changes, but in the mean time I suggest you formulate a good reason to keep the mixed library feature if it is important for your workflow, and you can't do without jellyfin/jellyfin-meta#46