XMP sidecars for video files can't show correctly only one keyword

[kagahd]

Describe the bugs

While I appreciate a lot the implementation of #761 to support XMP sidecars for video files (thanks a lot @grahamalderson for your great work!), I may have spotted 2 bugs:

1. If the tagged video contains only one keyword, the keyword is shown in PiGallery2 character by character, each prefixed by a hash sign, all separated by comma and space (see screenshot below).
2. If the xmp file does not include the file extension of the tagged file, no keywords and ratings are shown in PiGallery's frontend. While I see in the commit here and here that xmp files without file extension of the tagged file should be picked up as well, it did not work for me. If I renamed the file bunny.mp4.xmp to bunny.xmp, PiGallery's frontend did not show keywords and ratings for the bunny.mp4 video anymore.

Photo/video that causes the bug

I think it's independent of the video file since metadata is extracted from the xmp file. I reproduced with my own videos but also with the PiGallery2 demo video.
If I remove line 21 of its xmp file in order to have only one instead of two keywords, it would look like this:

 <rdf:Description rdf:about=''
  xmlns:dc='http://purl.org/dc/elements/1.1/'>
  <dc:format>H.264</dc:format>
  <dc:subject>
   <rdf:Bag>
    <rdf:li>rabbit</rdf:li>
   </rdf:Bag>
  </dc:subject>
 </rdf:Description>

With this xmp file, PiGallery2 would show #r, #a, #b, #b, #i, #t instead of just rabbit.

Screenshots

Environment:

• OS: MacOS Ventura 13.6.4
• Browser: Chrome

Used app version:

• Docker images:
  • bpatrik/pigallery2:edge-debian-buster
  • bpatrik/pigallery2:edge-debian-bullseye
  • bpatrik/pigallery2:edge-alpine
• Git commit: d1684d4

[kagahd]

PR #839 fixes both bugs.