fix(callable): __call cannot be in a nested metatable

[Tieske]

if a metatable doesn't itself have a __call function, but gets one through another metatable, then the original object is NOT callable. Lua will query the metatable using rawget, and hence will not return the nested __call function

Reported by @tmillr here

[alerque]

Is this true for all relevant versions of the Lua VM?

[Tieske]

@alerque I updated the test by actually calling it to verify it is non-callable. Passes on all the engines.