tdf#107644: Crash on inserting formula

See https://bugs.documentfoundation.org/attachment.cgi?id=133085
Accessibility related

Change-Id: I87063e50a59b06f4f5a974764de9aa34e111b4fb
Reviewed-on: https://gerrit.libreoffice.org/37315Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: sam tygier <samtygier@yahoo.co.uk>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Julien Nabet <serval2412@yahoo.fr>

starmath/source/accessibility.cxx

@@ -392,7 +392,7 @@ void SAL_CALL SmGraphicAccessible::addAccessibleEventListener(
 void SAL_CALL SmGraphicAccessible::removeAccessibleEventListener(
         const Reference< XAccessibleEventListener >& xListener )
 {
-    if (xListener.is())
+    if (xListener.is() && nClientId)
     {
         SolarMutexGuard aGuard;
         sal_Int32 nListenerCount = comphelper::AccessibleEventNotifier::removeEventListener( nClientId, xListener );