tdf#121323 avoid fatal exception with a11y enabled

not related to the problem described there, but worth avoiding

Change-Id: I5a33425d856d1a2d31a4e735b9936a89576121b3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103176
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
diff --git a/svx/source/accessibility/ChildrenManagerImpl.cxx b/svx/source/accessibility/ChildrenManagerImpl.cxx
index b24f706..dbfeb7c 100644
--- a/svx/source/accessibility/ChildrenManagerImpl.cxx
+++ b/svx/source/accessibility/ChildrenManagerImpl.cxx
@@ -294,7 +294,7 @@ void ChildrenManagerImpl::CreateListOfVisibleShapes (
    }

    // Add the visible shapes for which only the XShapes exist.
    if (mxShapeList.is())
    if (mxShapeList.is() && mxShapeList->hasElements())
    {
        sal_Int32 nShapeCount = mxShapeList->getCount();
        raDescriptorList.reserve( nShapeCount );
@@ -321,7 +321,6 @@ void ChildrenManagerImpl::CreateListOfVisibleShapes (
    }
}


void ChildrenManagerImpl::RemoveNonVisibleChildren (
    const ChildDescriptorListType& rNewChildList,
    ChildDescriptorListType& rOldChildList)