correctly remove tooltips when their snap elements get removed

Author: Ellpeck

MLEM.Ui/Elements/Tooltip.cs

@@ -226,6 +226,10 @@ public void SnapPositionToMouse() {
 
             var snapEl = this.SnapElement ?? this.autoNavSnapElement;
             if (snapEl != null) {
+                if (snapEl.Root == null) {
+                    this.Remove();
+                    return;
+                }
                 snap = this.GetSnapOffset(this.AutoNavAnchor, snapEl.DisplayArea, this.AutoNavOffset) / this.Scale;
             } else {
                 var mouseBounds = new RectangleF(this.SnapPosition ?? this.Input.ViewportMousePosition.ToVector2(), Vector2.Zero);
@@ -306,6 +310,11 @@ public void AddToElement(Element elementToHover) {
                     this.autoNavSnapElement = null;
                 }
             };
+
+            elementToHover.OnRemovedFromUi += e => {
+                this.Remove();
+                this.autoNavSnapElement = null;
+            };
         }
 
         private void Init(Element elementToHover) {