Trying to call a null function in Lua gives a bad error message

After @basicer's recent change to save the Lua parser from generating code from bad player code that crashes escodegen, at least it doesn't hang, but we give a bad error message for trying to call a nil function like this:

``` lua
a = function() end
a():b()
```

or

``` lua
a = {}
a:b:c()
```

result in error messages where it tells you the name of the nil thing is __luaTemp$1234.
