imap: Set command start timestamps earlier.

Previously timing statistics in taglines weren't shown commands that didn't
read any parameters.

Also the timings now include the time speng reading command parameters from
client. For example:

a list "" {1}
+ OK
%
* LIST (\HasNoChildren) "/" INBOX
a OK List completed (0.001 + 1.214 secs).

src/imap/imap-client.c

@@ -584,9 +584,6 @@ bool client_read_args(struct client_command_context *cmd, unsigned int count,
 		str = t_str_new(256);
 		imap_write_args(str, *args_r);
 		cmd->args = p_strdup(cmd->pool, str_c(str));
-		cmd->start_time = ioloop_timeval;
-		cmd->start_ioloop_wait_usecs =
-			io_loop_get_wait_usecs(current_ioloop);
 
 		cmd->client->input_lock = NULL;
 		return TRUE;
@@ -723,6 +720,8 @@ struct client_command_context *client_command_alloc(struct client *client)
 	cmd = p_new(client->command_pool, struct client_command_context, 1);
 	cmd->client = client;
 	cmd->pool = client->command_pool;
+	cmd->start_time = ioloop_timeval;
+	cmd->start_ioloop_wait_usecs = io_loop_get_wait_usecs(current_ioloop);
 	p_array_init(&cmd->module_contexts, cmd->pool, 5);
 
 	DLLIST_PREPEND(&client->command_queue, cmd);