TooltipWindow: Avoid potential use-after-free of lastComponentUnderMouse

Showing the tip will in turn call getDesktopScaleFactor(), accessing the
lastComponentUnderMouse. In some cases, it was possible for
lastComponentUnderMouse to point to a deleted component, resulting in
UB.

There are two changes in this PR:
- Using a SafePointer rather than a raw pointer ensures that calls to
  getDesktopScaleFactor() will always be safe, regardless of when they
  happen.
- Moving the assignment of lastComponentUnderMouse to before the call to
  displayTipInternal() ensures that the returned scale factor is that of
  the component that the mouse is currently hovering.

modules/juce_gui_basics/windows/juce_TooltipWindow.cpp

@@ -218,6 +218,9 @@ void TooltipWindow::timerCallback()
         const auto tipChanged = (newTip != lastTipUnderMouse || newComp != lastComponentUnderMouse);
         const auto now = Time::getApproximateMillisecondCounter();
 
+        lastComponentUnderMouse = newComp;
+        lastTipUnderMouse = newTip;
+
         if (tipChanged || dismissalMouseEventOccurred || mouseMovedQuickly)
             lastCompChangeTime = now;
 
@@ -246,9 +249,6 @@ void TooltipWindow::timerCallback()
                 showTip();
             }
         }
-
-        lastComponentUnderMouse = newComp;
-        lastTipUnderMouse = newTip;
     }
 }
 

modules/juce_gui_basics/windows/juce_TooltipWindow.h

@@ -136,7 +136,7 @@ public:
 private:
     //==============================================================================
     Point<float> lastMousePos;
-    Component* lastComponentUnderMouse = nullptr;
+    SafePointer<Component> lastComponentUnderMouse;
     String tipShowing, lastTipUnderMouse, manuallyShownTip;
     int millisecondsBeforeTipAppears;
     unsigned int lastCompChangeTime = 0, lastHideTime = 0;