copy-to-clipboard command error if mpv is idle

[itsmeipg]

Happens when uosc is idle or before a YouTube video fully loads.
Expected behavior: copy-to-clipboard does nothing or says something like "Nothing to copy"

[uosc] stack traceback:
[uosc]  ...241124-git-2d813de/portable_config/scripts/uosc/main.lua:1128: in function 'callback'
[uosc]  ...241124-git-2d813de/portable_config/scripts/uosc/main.lua:895: in function 'fn'
[uosc]  mp.defaults:235: in function 'fn'
[uosc]  mp.defaults:66: in function 'handler'
[uosc]  mp.defaults:388: in function 'handler'
[uosc]  mp.defaults:522: in function 'call_event_handlers'
[uosc]  mp.defaults:564: in function 'dispatch_events'
[uosc]  mp.defaults:515: in function <mp.defaults:514>
[uosc]  [C]: at 0x7ff6c3d6ee50
[uosc]  [C]: at 0x7ff6c3d6dc70
[uosc] Lua error: ...4-git-2d813de/portable_config/scripts/uosc/lib/utils.lua:895: attempt to concatenate local 'payload' (a nil value)