This commit contributes to handling wmNotify event for tooltip of a Tree
regardless of if the Tree object maintains the handle of the tooltip in
itemToolTipHandle. If there's a tooltip which is not handled by
wmNotifyToolTip, it is completely maintained by windows and hence can
span over multiple montiors. Hence, with this PR such tooltips are also
positioned inside a single monitor to prevent any infinite loop.

Contributes to
https://github.com/eclipse-platform/eclipse.platform.swt/issues/62 and
https://github.com/eclipse-platform/eclipse.platform.swt/issues/128