Fix possible buffer overrun in hba.c.

Coverty reports a possible buffer overrun in the code that populates the
pg_hba_file_rules view.  It may not be a live bug due to restrictions
on options that can be used together, but let's increase MAX_HBA_OPTIONS
and correct a nearby misleading comment.

Back-patch to 10 where this code arrived.

Reported-by: Julian Hsiao
Discussion: https://postgr.es/m/CADnGQpzbkWdKS2YHNifwAvX5VEsJ5gW49U4o-7UL5pzyTv4vTg%40mail.gmail.com

src/backend/libpq/hba.c

@@ -2218,10 +2218,12 @@ load_hba(void)
 /*
  * This macro specifies the maximum number of authentication options
  * that are possible with any given authentication method that is supported.
- * Currently LDAP supports 10, so the macro value is well above the most any
- * method needs.
+ * Currently LDAP supports 11, and there are 3 that are not dependent on
+ * the auth method here.  It may not actually be possible to set all of them
+ * at the same time, but we'll set the macro value high enough to be
+ * conservative and avoid warnings from static analysis tools.
  */
-#define MAX_HBA_OPTIONS 12
+#define MAX_HBA_OPTIONS 14
 
 /*
  * Create a text array listing the options specified in the HBA line.
@@ -2327,6 +2329,7 @@ gethba_options(HbaLine *hba)
 				CStringGetTextDatum(psprintf("radiusports=%s", hba->radiusports_s));
 	}
 
+	/* If you add more options, consider increasing MAX_HBA_OPTIONS. */
 	Assert(noptions <= MAX_HBA_OPTIONS);
 
 	if (noptions > 0)