Utils: fix crash on hiding a tooltip

Closing the tip label indirectly calls ToolTip::hideTipImmediately via
its eventFilter that closes the tool tip on any FocusIn/Out event on the
application. Since m_tip is reset in hideTipImmediately the outer call
crashes when this nullptr gets dereferenced. Avoid this crash by
resetting m_tip before closing the tip label.

Fixes: QTCREATORBUG-30738
Change-Id: Id3e690141be196db8ac6c4dab3d97627c0657140
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/tooltip/tooltip.cpp

@@ -288,9 +288,11 @@ void ToolTip::hideTipWithDelay()
 void ToolTip::hideTipImmediately()
 {
     if (m_tip) {
-        m_tip->close();
-        m_tip->deleteLater();
-        m_tip = nullptr;
+        TipLabel *tip = m_tip.data();
+        m_tip.clear();
+
+        tip->close();
+        tip->deleteLater();
     }
     m_showTimer.stop();
     m_hideDelayTimer.stop();