fix(UIPointer): repetitive enter events

When hovering over elements where ExecuteEvents.ExecuteHierarchy does
not return a target, the Enter event would fire repetitively. This
change ensures the event only fires once for these types of elements.
The reason this was happening was because the `pointerEventData` was
not being set properly when firing enter for these elements and would
trigger again the next time Hover was called.

Thanks to @kristianpd for the work on this fix.

Author: thestonefox

Assets/VRTK/Source/Scripts/Internal/VRTK_VRInputModule.cs

@@ -137,6 +137,8 @@ protected virtual void Hover(VRTK_UIPointer pointer, List<RaycastResult> results
                     }
 
                     GameObject target = ExecuteEvents.ExecuteHierarchy(result.gameObject, pointer.pointerEventData, ExecuteEvents.pointerEnterHandler);
+                    target = (target == null ? result.gameObject : target);
+
                     if (target != null)
                     {
                         Selectable selectable = target.GetComponent<Selectable>();
@@ -159,14 +161,12 @@ protected virtual void Hover(VRTK_UIPointer pointer, List<RaycastResult> results
                         pointer.pointerEventData.hovered.Add(pointer.pointerEventData.pointerEnter);
                         break;
                     }
-                    else
+
+                    if (result.gameObject != pointer.hoveringElement)
                     {
-                        if (result.gameObject != pointer.hoveringElement)
-                        {
-                            pointer.OnUIPointerElementEnter(pointer.SetUIPointerEvent(result, result.gameObject, pointer.hoveringElement));
-                        }
-                        pointer.hoveringElement = result.gameObject;
+                        pointer.OnUIPointerElementEnter(pointer.SetUIPointerEvent(result, result.gameObject, pointer.hoveringElement));
                     }
+                    pointer.hoveringElement = result.gameObject;
                 }
 
                 if (pointer.hoveringElement && results.Count == 0)