Incorrect [Using undefined variable] error on unassigned variable declarations in autoconcat (non-strict mode)

When having variable declarations in a script where that variable might never be assigned to, then an incorrect `Using undefined variable: @var` runtime error is given if that declaration is inside an autoconcat.
Example code:
```
string @var;
msg();
```

Problem:
__autoconcat__() gets the value of declaration `string @var`, causing this runtime error.