Fix mouse wheel scrolling not working on FlxInputText

[Starmapo]

Like the title says, this fixes the input text not scrolling when using the mouse wheel on it. This can be seen with just a regular text input object with multiline enabled:

var text = new FlxInputText(5, 5, FlxG.width - 20, "Hello world!", 16);
text.fieldHeight = 44;
text.multiline = true;
add(text);

I also added a comment with information on the fix.

[Geokureli]

Thanks!