For now, work around sporadic SwNoTxtFrm::Modify failures

...that appear sporadically in the wild but are decently reproducible at least
on OS X when changing the DoUpdateModifiedOLE timeout in the SwDoc ctor
(sw/source/core/doc/docnew.cxx) from 1000 to 100 when running
CppunitTest_writerperfect_writer, caused by a bad static cast from an SwOLENode
to an SwGrfNode at

SwNoTxtFrm::Modify
SwModify::ModifyBroadcast
SwModify::NotifyClients
SwCntntNode::Modify
SwClient::ModifyNotification
SwDoc::DoUpdateModifiedOLE
SwDoc::LinkStubDoUpdateModifiedOLE
Link::Call
Timer::Timeout
Timer::ImplTimerCallbackProc
SalTimer::CallCallback
-[TimerCallbackCaller timerElapsed:]
[...]
-[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:]
AquaSalInstance::AnyInput
Application::AnyInput
SwLayAction::CheckIdleEnd
SwLayAction::_FormatFlyCntnt
SwObjectFormatter::_FormatObj
SwObjectFormatterLayFrm::DoFormatObj
SwObjectFormatter::_FormatObjsAtFrm
SwObjectFormatterLayFrm::DoFormatObjs
SwObjectFormatter::FormatObjsAtFrm
SwLayAction::InternalAction
SwLayAction::Action
SwViewShell::ImplEndAction
SwViewShell::EndAction
SwCrsrShell::EndAction
SwRootFrm::EndAllAction
UnoActionContext::~UnoActionContext
UnoActionContext::~UnoActionContext
SwXTextDocument::unlockControllers
writerperfect::test::WpftImportTestBase::load
[...]

Change-Id: I8903cf6890c3cf526768939dca2438fa2d978310