Protection for calling null function

[crosslife]

eg.

state"null_func"

[ThePhD]

Should this be a no-op or should it error? My personal belief is that it should error.

[jeremyong]

Prefer error or exception for sure. I haven't thought of the ideal way to handle this. It could silently fill an error register in the background and not crash the program but this would require safe usage of the library to check this register after every operation. Undecided as of this moment what the right thing to do is.

[jeremyong]

I plan on changing all calls to lua_call to lua_pcall nested with appropriate assertions.