Fix interop issue with mpv-gallery-view

[Holi0317]

I am quite new to mpv and may have done this fix incorrectly. Please check before merging.

After installing both occivink/mpv-gallery-view and this plugin, error will be thrown when gallery view is launched.

Traceback:

[mpv_thumbnail_script_client_osc]
[mpv_thumbnail_script_client_osc] stack traceback:
[mpv_thumbnail_script_client_osc]       .../.config/mpv/scripts/mpv_thumbnail_script_client_osc.lua:1080: in function 'prop'
[mpv_thumbnail_script_client_osc]       mp.defaults:365: in function 'handler'
[mpv_thumbnail_script_client_osc]       mp.defaults:458: in function 'call_event_handlers'
[mpv_thumbnail_script_client_osc]       mp.defaults:495: in function 'dispatch_events'
[mpv_thumbnail_script_client_osc]       mp.defaults:451: in function <mp.defaults:450>
[mpv_thumbnail_script_client_osc]       [C]: in ?
[mpv_thumbnail_script_client_osc]       [C]: in ?
[mpv_thumbnail_script_client_osc] Lua error: .../.config/mpv/scripts/mpv_thumbnail_script_client_osc.lua:1080: attempt to compare nil with number

This patch add nil check on duration variable and fix the issue.

---

Other than this issue, I got issue with thumbnail generation on short video (Videos that will generate less than 150 thumbnails, which is the thumbnail_count config)

Mpv log says output file missing while the log file for converter says the following:

[   0.080][v][mkv] EOF reached.
[   0.106][v][cplayer] video EOF reached
[   0.106][v][cplayer] playback restart complete
[   0.106][v][cplayer] EOF code: 1
[   0.106][v][vd] Uninit video.
[   0.107][v][cplayer] finished playback, no audio or video data played (reason 4)
[   0.107][i][cplayer]
[   0.107][i][cplayer]
[   0.107][i][cplayer] Exiting... (Errors when loading file)

I am not sure if that is my fault or issue with server module.

Thanks

[TheAMM]

Hm. I'll have to look at this myself, later, because the state.ready should only be true when it truly is ready.
get_delta() returns nil if the duration is not available, and we ensure we have a delta on this line. Maybe the listeners are executed out of order, despite the docs.

What "short file" were you using? Some files are broken; seeking to their end will fail. I've ran into so few of them I kept the bail instead of padding them with black.

[Holi0317]

Thanks.

I have tried some videos from youtube but only videos uploaded from this guy (Sorry but that channel is speaking Cantonese) in has this issue.

Sample video. Just download it using youtube-dl (not in streaming mode) and open with mpv. The bug will occur. Other "Short files" does not have the issue.

If you cannot reproduce it, I can sent you my copy of the video.

Gist for logs

[TheAMM]

Merged #43 which deals with the same issue.