skip groups not listed in active file

tin currently sends out GROUP cmds. for every group in the newsrc (in the
"-n -l" case which is default) even if that group is not listed in the servers
active file. this causes problems on some servers as the group may exist but
is restricted (it hidden from the active file if not authentiacted) and the
server may respond with 502. the small patch below should solve that
problem by skipping GROUP for groups not listed in the active file if tin
is running with "-n -l". (in the -l only case we don't send GROUP at all and
in the -n only case we don't have the active file).

=== modified file 'src/active.c'
--- src/active.c	2010-03-19 23:11:02 +0000
+++ src/active.c	2010-09-23 09:51:09 +0000
@@ -361,7 +361,7 @@
 #ifdef NNTP_ABLE
 			char buf[NNTP_STRLEN];
 			char line[NNTP_STRLEN];
-			if (window < NUM_SIMULTANEOUS_GROUP_COMMAND && ptr) {
+			if (window < NUM_SIMULTANEOUS_GROUP_COMMAND && ptr && (!list_active || (newsrc_active && list_active && group_find(ptr, FALSE)))) {
 				ngnames[index_i] = my_strdup(ptr);
 				snprintf(buf, sizeof(buf), "GROUP %s", ngnames[index_i]);
 #	ifdef DEBUG