Avoid UBSan "left shift of 65536 by 16 places cannot be represented...

...in type 'int'" warning when constructing an XML_TOKEN_MAP_END instance, whose
nPrefixKey is 0xffffU.  Problem got introduced with
41b3fd8c "Make SvXMLTokenMap compatible with
FastTokens", the intent was presumably to make the shifted value of

  ( nPrefixKey + 1 ) << 16

be zero in that case.

Change-Id: I0b83a03198a44e54077899e4484634286d06cdcc

include/xmloff/xmltkmap.hxx

@@ -44,7 +44,7 @@ struct SvXMLTokenMapEntry
         nPrefixKey( nPrefix ),
         eLocalName( eName ),
         nToken( nTok ),
-        nFastToken( ( nPrefixKey + 1 ) << 16 | eLocalName )
+        nFastToken( sal_uInt32( nPrefixKey + 1 ) << 16 | eLocalName )
     {
         if ( nFastTok )     // alternative value for duplicate/dummy tokens
             nFastToken = nFastTok;