Fix crash when error()ing an invalid value

[cheapie]

No description provided.

[sofar]

👍

[Desour]

Could you please use tostring instead of dump? Now it adds extra "s and if it's a table, it would give new lines that don't fit into the formspec.
Perhaps something like errmsg and (tostring(errmsg) or dump(errmsg)) or "".

[numberZero]

@DS-Minetest Er, the error message is unreadable anyway, so its formatting, basically, doesn’t matter. The crash must be prevented.

[Desour]

Actually the error messages are readable and useful IMO and using tostring would also fix the bug.

[numberZero]

564bdc2
As error() expects a message (that is, a string), handling of non-string values may be arbitrary as long as it works somehow.