vcl: fix online crash in vcl::Window::IsTracking()

vcl: fix online crash in vcl::Window::IsTracking()

Crashreport signature:

program/libmergedlo.so
	vcl::Window::IsTracking() const
		vcl/source/window/window2.cxx:340
program/libmergedlo.so
	(anonymous namespace)::LOKPostAsyncEvent(void*, void*)
		sfx2/source/view/lokhelper.cxx:812
program/libmergedlo.so
	LokChartHelper::postMouseEvent(int, int, int, int, int, int, double, double)
		include/rtl/ref.hxx:128
program/libmergedlo.so
	SfxLokHelper::testInPlaceComponentMouseEventHit(SfxViewShell*, int, int, int, int, int, int, double, double, bool)
		sfx2/source/view/lokhelper.cxx:980
/program/libswlo.so
	SwXTextDocument::postMouseEvent(int, int, int, int, int, int)
		sw/source/uibase/uno/unotxdoc.cxx:3663
program/libmergedlo.so
	doc_postMouseEvent
		desktop/source/lib/init.cxx:4831

Change-Id: Iab7d24a901e57dc8af3fb2c77fbea3b4fdad9fb9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/146483
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/146549
Tested-by: Jenkins
Reviewed-by: Andras Timar <andras.timar@collabora.com>