Fix layer selection on delete

Sources/arm/data/LayerSlot.hx

@@ -100,7 +100,7 @@ class LayerSlot {
 		var lpos = Project.layers.indexOf(this);
 		Project.layers.remove(this);
 		// Undo can remove base layer and then restore it from undo layers
-		if (lpos > 0) Context.setLayer(Project.layers[lpos - 1]);
+		Context.setLayer(Project.layers[lpos > 0 ? lpos - 1 : 0]);
 	}
 
 	public function unload() {

Sources/arm/ui/TabLayers.hx

@@ -307,6 +307,7 @@ class TabLayers {
 								if (l.parent != null && l.parent.getChildren() == null) {
 									l.parent.delete();
 								}
+								Context.ddirty = 2;
 							}
 						}
 						if (ui.button(tr("Move Up"), Left)) {