simplify a conditional expression using S_OR

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@77630 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -17455,10 +17455,7 @@ static int reload_config(enum channelreloadreason reason)
 	global_allowsubscribe = FALSE;
 	snprintf(global_useragent, sizeof(global_useragent), "%s %s", DEFAULT_USERAGENT, ASTERISK_VERSION);
 	ast_copy_string(default_notifymime, DEFAULT_NOTIFYMIME, sizeof(default_notifymime));
-	if (ast_strlen_zero(ast_config_AST_SYSTEM_NAME))
-		ast_copy_string(global_realm, DEFAULT_REALM, sizeof(global_realm));
-	else
-		ast_copy_string(global_realm, ast_config_AST_SYSTEM_NAME, sizeof(global_realm));
+	ast_copy_string(global_realm, S_OR(ast_config_AST_SYSTEM_NAME, DEFAULT_REALM), sizeof(global_realm));
 	ast_copy_string(default_callerid, DEFAULT_CALLERID, sizeof(default_callerid));
 	compactheaders = DEFAULT_COMPACTHEADERS;
 	global_reg_timeout = DEFAULT_REGISTRATION_TIMEOUT;