coverity#704774 Explicit null dereferenced

Change-Id: Ief63d63233d11015f64f5e6a19544889f0389ca3
Reviewed-on: https://gerrit.libreoffice.org/2870Reviewed-by: Noel Power <noel.power@suse.com>
Tested-by: Noel Power <noel.power@suse.com>

sd/source/ui/view/OutlinerIterator.cxx

@@ -757,6 +757,10 @@ void ViewIteratorImpl::Reverse (void)
     // Move iterator to the current object.
     SdrObjectWeakRef xObject = maPosition.mxObject;
     maPosition.mxObject.reset(NULL);
+
+    if (!mpObjectIterator)
+        return;
+
     while (mpObjectIterator->IsMore() && maPosition.mxObject != xObject)
         maPosition.mxObject.reset(mpObjectIterator->Next());
 }