sfx2: fix crash in SfxLokHelper::notifyAllViews(...)

Crashreport signature:

program/libmergedlo.so
	SfxLokHelper::notifyAllViews(int, rtl::OString const&)
		sfx2/source/view/lokhelper.cxx:682
program/libmergedlo.so
	SfxClipboardChangeListener::ChangedContents()
		include/rtl/string.hxx:413
program/libmergedlo.so
	SfxClipboardChangeListener::LinkStubAsyncExecuteHdl_Impl(void*, void*)
		include/rtl/ref.hxx:128
program/libmergedlo.so
	ImplWindowFrameProc(vcl::Window*, SalEvent, void const*)
		include/rtl/ref.hxx:128
program/libmergedlo.so
	SvpSalInstance::ProcessEvent(SalUserEventList::SalUserEvent)

Change-Id: Ibf70f42292d67a3d6cc68f579ee02f671da85acb
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/146150
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
(cherry picked from commit dc17158c99c8a15fbca57a9a0b0ea7178dcc5a34)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/146400
Tested-by: Jenkins
Reviewed-by: Aron Budea <aron.budea@collabora.com>
diff --git a/sfx2/source/view/lokhelper.cxx b/sfx2/source/view/lokhelper.cxx
index 53c2aba..29f64ad 100644
--- a/sfx2/source/view/lokhelper.cxx
+++ b/sfx2/source/view/lokhelper.cxx
@@ -676,6 +676,8 @@ void SfxLokHelper::notifyAllViews(int nType, const OString& rPayload)

    const auto payload = rPayload.getStr();
    const SfxViewShell* const pCurrentViewShell = SfxViewShell::Current();
    if (!pCurrentViewShell)
        return;
    SfxViewShell* pViewShell = SfxViewShell::GetFirst();
    while (pViewShell)
    {