ofz+ubsan: runtime error: left shift cannot be represented in type

Change-Id: Ic153b39475abbd562e4c81b47089ca8280080cff
Reviewed-on: https://gerrit.libreoffice.org/43569Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sot/source/sdstor/stgstrms.cxx

@@ -71,8 +71,10 @@ rtl::Reference< StgPage > StgFAT::GetPhysPage( sal_Int32 nByteOff )
 
 sal_Int32 StgFAT::GetNextPage( sal_Int32 nPg )
 {
-    if( nPg >= 0 )
+    if (nPg >= 0)
     {
+        if (nPg > (SAL_MAX_INT32 >> 2))
+            return STG_EOF;
         rtl::Reference< StgPage > pPg = GetPhysPage( nPg << 2 );
         nPg = pPg.is() ? StgCache::GetFromPage( pPg, m_nOffset >> 2 ) : STG_EOF;
     }