fix bug

http/charge.js

@@ -817,7 +817,7 @@ proto.addUsdtAsync = P.coroutine(function* (query, method, res){var response = {
 		return this.writeOut(response, res);
 	}
 	var usdt_amount = query["usdt_amount"]
-	if (!usdt_amount || usdt_amount == 0) {
+	if (!usdt_amount) {
 		response.code = 401
 		response.message = "token invalid"
 		return this.writeOut(response, res);