ntpd timegm error checks

Another rather straightforward conversion, removing a confusing comment
that would become a bit more confusing.

As visible in the diff, tls_tm is parsed twice in a row, where the
second (rather the first) parse was added with the manual constraints
checking in 2019. The layering is a bit strange here.

Index: constraint.c
===================================================================
RCS file: /cvs/src/usr.sbin/ntpd/constraint.c,v
diff -u -p -r1.60 constraint.c
--- constraint.c	21 Nov 2024 13:38:14 -0000	1.60
+++ constraint.c	31 May 2026 10:14:09 -0000
@@ -1062,7 +1062,9 @@ httpsdate_request(struct httpsdate *http
 	 */
 	notbefore = tls_peer_cert_notbefore(httpsdate->tls_ctx);
 	notafter = tls_peer_cert_notafter(httpsdate->tls_ctx);
-	if ((httptime = timegm(&httpsdate->tls_tm)) == -1)
+	httpsdate->tls_tm.tm_wday = -1;
+	if ((httptime = timegm(&httpsdate->tls_tm)) == -1 &&
+	    httpsdate->tls_tm.tm_wday == -1)
 		goto fail;
 	if (httptime <= notbefore) {
 		if ((tm = gmtime(&notbefore)) == NULL)
@@ -1114,8 +1116,12 @@ httpsdate_query(const char *addr, const 
 	if (httpsdate_request(httpsdate, &when, synced) == -1)
 		return (NULL);
 
-	/* Return parsed date as local time */
+	httpsdate->tls_tm.tm_wday = -1;
 	t = timegm(&httpsdate->tls_tm);
+	if (t == -1 && httpsdate->tls_tm.tm_wday == -1) {
+		httpsdate_free(httpsdate);
+		return (NULL);
+	}
 
 	/* Report parsed Date: as "received time" */
 	rectv->tv_sec = t;