FlxBitmapText does not permit negative line spacing

[seraku24]

• Flixel version: 4.2.0
• OpenFL version: 3.6.1
• Lime version: 2.9.1
• Affected targets: flash, and (possibly) all others

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Code snippet reproducing the issue:

package;

import flixel.FlxG;
import flixel.FlxState;
import flixel.text.FlxBitmapText;

class PlayState extends FlxState
{
    override public function create():Void {
        var bitmapText = new FlxBitmapText();
        var desiredLineSpacing = -5;
        bitmapText.lineSpacing = desiredLineSpacing;
        if (bitmapText.lineSpacing != desiredLineSpacing) {
            FlxG.log.error("FlxBitmapText.lineSpacing is not desired value.");
        }
    }
}

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Observed behavior:
The lineSpacing property becomes a positive value, specifically the absolute value.

Expected behavior:
The lineSpacing property allows a negative value to be set.

NOTE: Near as I can tell, the text layout code in FlxBitmapText is already written properly to support a negative value for lineSpacing which would result in condensed spacing. The issue, then, lies within the property setter enforcing a positive-only value.

[Gama11]

This seems familiar. :) #1603