Subtitle offset not reset between files

[jjaine]

Test environment

PMS Version: Version 1.25.5.5492 (Running on Ubuntu 20.04)
PMP Version: 1.40.1.2823
Platform (Windows/macOS/Embedded RPi/Embedded Intel): Windows

Steps to reproduce

1. Play any video file with subtitles
2. Download external subtitles from OpenSubtitles
3. Adjust the subtitle offset
4. Start playing another video file with built-in subtitles or with subtitles downloaded from OpenSubtitles
5. See the subtitle offset carried over to the next file (UI shows 0ms as the offset, but the subtitle offset is wrong)
6. Resetting the subtitle offset (if possible) or restarting the PMP fixes the problem

Current behavior

1. Subtitle offset is carried over to next file

Expected behavior

1. Set subtitle offset is not applied to other media files