tdf#128502: Avoid potential crash in mobile app with multiple open documents

Not sure if actually needed, but can hardly harm.

Change-Id: Ibb819818db40b2f086e5c1f2330a7f8f2fcc1727
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/95148
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Andras Timar <andras.timar@collabora.com>
diff --git a/sc/source/ui/unoobj/docuno.cxx b/sc/source/ui/unoobj/docuno.cxx
index 96ce59f..c812682 100644
--- a/sc/source/ui/unoobj/docuno.cxx
+++ b/sc/source/ui/unoobj/docuno.cxx
@@ -541,7 +541,7 @@
int ScModelObj::getPart()
{
    ScViewData* pViewData = ScDocShell::GetViewData();
    return pViewData->GetViewShell()->getPart();
    return pViewData ? pViewData->GetViewShell()->getPart() : 0;
}

OUString ScModelObj::getPartInfo( int nPart )