mpv only sends the latest value of an observed property, and only after its
IPC thread has handled queued commands and events. A same-file
`loadfile replace` can therefore arrive with no `path=null`, so path
comparisons see no change, the autoplay gate stays released for that path and
drops every ready signal, and playback stays paused.
Track an `end-file` that mpv has not followed with a different path. If it is
still pending at `file-loaded`, replay the clear and read the path back, so
consumers see the same sequence as any other load. `file-loaded` waits for the
reply so plugins can read their media snapshot during the event.
Fixes#320
