If the tooltip exists, release its reference on exit instead of deleting it directly. Resolves a crash on exit if a tooltip was showing at the time.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@38361 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/preferences/time/ZoneView.cpp

@@ -92,7 +92,8 @@ TimeZoneView::CheckCanRevert()
 
 TimeZoneView::~TimeZoneView()
 {
-	delete fToolTip;
+	if (fToolTip)
+		fToolTip->ReleaseReference();
 }