blind fix MSVC werror C4701,C4703 potentially uninitialized local variable

... ´pModelObj´ used. Which is bullshit, but..

Change-Id: Ic731fc92264560c34bd512dc232a9ba901e218a5

sc/source/ui/view/tabview5.cxx

@@ -307,8 +307,8 @@ void ScTabView::TabChanged( bool bSameTabButMoved )
         ScDocShell* pDocSh;
         ScModelObj* pModelObj;
 
-        if ( ( pDocSh = GetViewData().GetDocShell() ) &&
-             ( pModelObj = ScModelObj::getImplementation( pDocSh->GetModel() )) )
+        if ( ( pDocSh = GetViewData().GetDocShell() ) != nullptr &&
+             ( pModelObj = ScModelObj::getImplementation( pDocSh->GetModel() )) != nullptr )
         {
             Size aDocSize = pModelObj->getDocumentSize();
             std::stringstream ss;