Bug: can't find sidecar file for MP4 associated with HEIC

[inakaboy]

most likely from Apple Live Photos, for example:

• IMG_0720.HEIC
• IMG_0720.HEIC.json
• IMG_0720.MP4
  // note that there is no IMG_0720.MP4.json file

Currently, the script fails to find the sidecar file for the MP4 component of the live photo due to this filename arrangement.
That should be fixed.

Also, maybe there should be an option to throw any images/videos for which sidecar files are not found into the errors directory, so these problems can be fixed manually.