[Flow] Fix line height of first line in multiline flow

[kLabz]

The issue can be easily reproduced with this sample:

import h2d.Tile;
import h2d.Bitmap;
import h2d.Flow;

class Main extends hxd.App {
	static public function main() {
		new Main();
	}

	override function init() {
		var flow = new Flow(s2d);
		flow.maxWidth = 200;
		flow.multiline = true;
		flow.debug = true;

		new Bitmap(Tile.fromColor(0xFF00FF, 200, 10), flow);
		new Bitmap(Tile.fromColor(0x00FFFF, 20, 40), flow);
		new Bitmap(Tile.fromColor(0xFFFF00, 10, 20), flow);

		var flow = new Flow(s2d);
		flow.maxWidth = 200;
		flow.multiline = true;
		flow.verticalAlign = Top;
		flow.x = 250;
		flow.debug = true;

		new Bitmap(Tile.fromColor(0x00FFFF, 200, 10), flow);
		new Bitmap(Tile.fromColor(0x00FFFF, 20, 40), flow);
		new Bitmap(Tile.fromColor(0xFFFF00, 10, 20), flow);
	}
}

Resetting maxLineHeight to 0 before positioning nodes makes sure previously calculated maxLineHeight isn't being used for first line when it should not.

Current heaps:

With this patch:

Tested with shiroTools 73faca1146

[ncannasse]

Shouldn't it also be done for columns in other align ?

[kLabz]

Probably indeed, will check that
Edit: yep, exact same issue with vertical layout, and exact same fix