fix a use-after-free in resolver

when processing a mismatched response, we call dns_dispatch_getnext().
If that fails, for example because of a timeout, fctx_done() is called,
which cancels all queries. This triggers a crash afterward when
fctx_cancelquery() is called, and is unnecessary since fctx_done()
would have been called later anyway.

lib/dns/resolver.c

@@ -9344,10 +9344,6 @@ rctx_next(respctx_t *rctx) {
 	INSIST(rctx->query->dispentry != NULL);
 	dns_message_reset(rctx->query->rmessage, DNS_MESSAGE_INTENTPARSE);
 	result = dns_dispatch_getnext(rctx->query->dispentry);
-	if (result != ISC_R_SUCCESS) {
-		fctx_done(rctx->fctx, result, __LINE__);
-	}
-
 	return (result);
 }