MDEV-25728: mysqld --help --verbose creates a log-bin-index file

before change test:

 strace -fe trace=file -o /tmp/f.strace sql/mysqld --datadir=/tmp/d --log-bin=foo-bin                      --help --verbose && ls -la /tmp/
...
'mysqladmin variables' instead of 'mysqld --verbose --help'.

total 0
drwxrwxr-x.  2 dan  dan   60 May 19 18:05 .
drwxrwxrwt. 27 root root 640 May 19 18:03 ..
-rw-rw----.  1 dan  dan    0 May 19 18:05 foo-bin.index

mysql-test/r/mysqld--help.result

@@ -1314,7 +1314,7 @@ lc-messages-dir MYSQL_SHAREDIR/
 lc-time-names en_US
 local-infile TRUE
 lock-wait-timeout 86400
-log-bin (No default value)
+log-bin foo
 log-bin-compress FALSE
 log-bin-compress-min-len 256
 log-bin-index (No default value)

mysql-test/t/mysqld--help.test

@@ -11,7 +11,7 @@
 # force symbolic-links=0 (valgrind build has a different default)
 #
 
-exec $MYSQLD_BOOTSTRAP_CMD --symbolic-links=0 --lower-case-table-names=1 --help --verbose > $MYSQL_TMP_DIR/mysqld--help.txt 2>&1;
+exec $MYSQLD_BOOTSTRAP_CMD --symbolic-links=0 --log-bin=foo --lower-case-table-names=1 --help --verbose > $MYSQL_TMP_DIR/mysqld--help.txt 2>&1;
 
 # The inline perl code below will copy $MYSQL_TMP_DIR/mysqld--help.txt
 # to output, but filter away some variable stuff (e.g. paths).

sql/mysqld.cc

@@ -5324,7 +5324,7 @@ static int init_server_components()
     }
   }
 
-  if (opt_bin_log)
+  if (!opt_help && opt_bin_log)
   {
     if (mysql_bin_log.open_index_file(opt_binlog_index_name, opt_bin_logname,
                                       TRUE))
@@ -5333,7 +5333,7 @@ static int init_server_components()
     }
   }
 
-  if (opt_bin_log)
+  if (!opt_help && opt_bin_log)
   {
     log_bin_basename=
       rpl_make_log_name(opt_bin_logname, pidfile_name,