popErrorScope status when stack is empty?

[kainino0x]

In JS when the error scope stack is empty, popErrorScope rejects with OperationError. What should we do in C?

Emscripten and Dawn currently translate it to Unknown plus a message string. However we also use Unknown in Emscripten if the error type is some unexpected object (e.g. if we add one to the JS API in the future).

We should also say what the message string is. I think it must be empty if the status is NoError and it should be non-empty for any other status. (since message can't be null anymore)

[lokokung]

Hmm, that's a good point. In C, there's only Success and InstanceDropped on WGPUPopErrorScopeStatus. Maybe we could add another case there instead of modifying the error type?