Don't allocate a group terminator unless we are in a group-list.

This will reduce memory allocation for garbage/spam address lists.

It also makes no sense to store a terminator when there wasn't a
display-name indicating the start of a group.

rfc822.c

@@ -461,7 +461,7 @@ add_addrspec (ADDRESS **top, ADDRESS **last, const char *phrase,
 
 ADDRESS *rfc822_parse_adrlist (ADDRESS *top, const char *s)
 {
-  int ws_pending, nl;
+  int ws_pending, nl, in_group = 0;
 #ifdef EXACT_ADDRESS
   const char *begin;
 #endif
@@ -551,6 +551,7 @@ ADDRESS *rfc822_parse_adrlist (ADDRESS *top, const char *s)
       terminate_buffer (phrase, phraselen);
       cur->mailbox = safe_strdup (phrase);
       cur->group = 1;
+      in_group = 1;
 
       if (last)
 	last->next = cur;
@@ -587,11 +588,12 @@ ADDRESS *rfc822_parse_adrlist (ADDRESS *top, const char *s)
 #endif
 
       /* add group terminator */
-      if (last)
+      if (last && in_group)
       {
 	last->next = rfc822_new_address ();
 	last = last->next;
       }
+      in_group = 0;
 
       phraselen = 0;
       commentlen = 0;