Jellyfin answers PlaybackInfo with a null DefaultSubtitleStreamIndex when the
user's SubtitleMode is None: the index is the server's whole answer, and null
means it picked no subtitle. The mapper read null as "the server did not say"
and promoted the container's default/forced flags to a server selection
instead, which outranks the profile subtitle mode in the selection ladder. A
viewer who had turned subtitles off for their Jellyfin user got them switched
back on by every item that carried a default or forced row.
Only the row the server names is selected now. A stream the viewer picks, and
an explicit off, still survive per item because Plezy reports the index
through playback progress and the server hands it back as that index or -1.
close#1779
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