Don't reference temporaries when using intToString

The following code that we use a lot is undefined behavior:
```c
paramValues[1] = intToString(index).strValue;
```
Instead it should be:
```c
IntString indexStr = intToString(index);
paramValues[1] = indexStr.strValue;
```

With the current code we're referencing temporaries, which can lead to all kinds of weird bugs.

Useful source: https://stackoverflow.com/a/17903361/2570866