When using --keep-open, and the end of the file is reached, the player's
"pause" property is set to true. Attempting to set it to false reverts
it back to true immediately. That's how it's designed, for better or
worse.
Running "seek -10 ; set pause no" did not work, because the seek is
first queued and pause is unset, but then the decoding functions
determine that EOF is still a thing, and "mpctx->stop_play =
AT_END_OF_FILE;" is set again. handle_keep_open() then sets pause again.
Only then the seek is actually run.
Fix this by not setting stop_play if a seek is queued.