$NetBSD: patch-mergequeries-boundscheck,v 1.1 2018/09/28 20:36:24 schmonz Exp $

Add a missing bounds check to the MERGEQUERIES patch's try_merge().
From Tim Stewart in <https://marc.info/?l=djbdns&m=153020962703821>

--- dns_transmit.c.orig	2018-09-28 20:25:42.000000000 +0000
+++ dns_transmit.c
@@ -35,6 +35,7 @@ static int try_merge(struct dns_transmit
   for (i = 0; i < MAXUDP; i++) {
     if (!inprogress[i]) continue;
     if (!merge_equal(d, inprogress[i])) continue;
+    if (inprogress[i]->nslaves == MAXUDP) continue;
     d->master = inprogress[i];
     inprogress[i]->slaves[inprogress[i]->nslaves++] = d;
     return 1;
@@ -127,8 +128,10 @@ static void mergefree(struct dns_transmi
   }
   /* and unregister all of our slaves from us */
   for (i = 0; i < d->nslaves; i++) {
-    if (d->slaves[i])
+    if (d->slaves[i]) {
       d->slaves[i]->master = NULL;
+      d->slaves[i] = 0;
+    }
   }
   d->nslaves = 0;
 }