configfiles: don't save negative start values

[guidocella]

When you seek to the beginning of paused audio without video, the pts becomes negative, and if you then quit-watch-later, when mpv restarts playback it seeks to the end of the file and immediately advances to the next playlist entry. Fix this by making the pts 0 in this case.

Partial fix of #10346.

[github-actions[bot]]

Download the artifacts for this pull request:

Windows

• mpv-i686-w64-mingw32
• mpv-x86_64-w64-mingw32
• mpv-x86_64-windows-msvc

macOS

• mpv-macos-12-intel
• mpv-macos-13-intel
• mpv-macos-14-arm

[Dudemanguy]

Superseded by https://github.com/mpv-player/mpv/pull/14227.