fixed clumsy error in detecting bad printitems..

m2decs.c

@@ -648,11 +648,11 @@ static void write_all_params( dname, s ) char *dname; shape s;
 			{
 				int n = pl->item->num;
 
-				for( p = s->params; --n; p = p->next )
-				{
+				for( p = s->params;
+				     p != NULL && --n;
+				     p = p->next );
 ASSERT( p != NULL,
 ("m2datadec: bad printitem number in shape %s of type %s\n", s->name, dname));
-				}
 				write_param( s->name, p );
 			}
 		}