Notify user when trying to free locked references.

[Faless]

This explains #33279 , #33290 . Demos will need to be fixed too if this is confirmed to be the desired approach.

The reference will not be freed when debug is enabled, causing a memory leak as explained by the message.

Needs review from @reduz : I hope I understood well what you suggested.

[capnm]

👍 Has already caught mistakes in my network script:

E 0:08:35:0245   unreference: Reference is locked and can't be freed. You are leaking memory! This will likely cause crashes in release builds.
  <C++ Error>    Condition ' _is_locked() && die ' is true. returned: false
  <C++ Source>   core/reference.cpp:100 @ unreference()
  <Stack Trace>  Lobby.gd:244 @ server_disconnected()

…

[qarmin]

I think that this can be closed because signal checking was (re)added here - 22637be

[Faless]

Yep, closing, thanks