Fix: panics with invalid ss url (https://github.com/xjasonlyu/tun2socks/issues/49)

engine/parse.go

@@ -73,9 +73,11 @@ func parseShadowsocks(u *url.URL) (address, method, password, obfsMode, obfsHost
 	} else {
 		data, _ := base64.RawURLEncoding.DecodeString(u.User.String())
 		userInfo := strings.SplitN(string(data), ":", 2)
+		if len(userInfo) == 2 {
 			method = userInfo[0]
 			password = userInfo[1]
 		}
+	}
 
 	rawQuery, _ := url.QueryUnescape(u.RawQuery)
 	for _, s := range strings.Split(rawQuery, ";") {