frontend/define.c, ntharg(), #6/15 rewrite while() --> for(;;)

src/frontend/define.c

@@ -408,7 +408,10 @@ static struct pnode *
 ntharg(int num, struct pnode *args)
 {
     // fact: num >= 1 for all known invocations of ntharg()
-        while (--num > 0) {
+        for (;;) {
+            if (--num <= 0) {
+                break;
+            }
             if (args && args->pn_op && (args->pn_op->op_num != PT_OP_COMMA)) {
                 if (num <= 1)
                     break;