Set the stack to zero before trying to optimize the datatype.

This commit was SVN r6008.

src/datatype/dt_optimize.c

@@ -50,6 +50,7 @@ int32_t ompi_ddt_optimize_short( ompi_datatype_t* pData, int32_t count,
     }
 
     pStack = alloca( sizeof(dt_stack_t) * (pData->btypes[DT_LOOP]+2) );
+    SAVE_STACK( pStack, 0, 0, 0, 0, 0 );
     total_disp = 0;
 
     pTypeDesc->length = 2 * pData->desc.used + 1 /* for the fake DT_END_LOOP at the end */;