cdn: 规范化 query 参数处理

[anxinxu]

Description

his PR tightens query-string handling when building CDN request URLs in Client (steam/cdn).

Empty query: If the optional query argument is an empty string, it is treated as “no query” and no query parameters are appended (avoids pointless work and odd ?-only URLs).
Leading ?: If the string starts with ?, that prefix is stripped before splitting on &, so callers can pass either foo=bar or ?foo=bar and get the same parsed parameters.
No README or public API changes.

Checklist

• Code compiles correctly
• All tests passing
• Samples run successfully
• Extended the README / documentation, if necessary

[anxinxu]

@LossyDragon Could a maintainer please approve the workflows for this fork PR? Thanks.

[LossyDragon]

If I understand your PR correctly, wouldn't val params = queryString.trimStart('?').split("&") suffice as well?

[anxinxu]

If I understand your PR correctly, wouldn't val params = queryString.trimStart('?').split("&") suffice as well?

Yes, I've changed it like this now