[error] [TilesetJsonLoader.cpp:1004] Received status code 404 for tile content file

### What happened?

3dtiles 包含+ 号的加载不了，识别有问题

### Environment

Cesium for Unity version:1.16
Unity Editor Version:6.1
Operating System:windows11

### Reproduction steps

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### Supporting evidence

_No response_

Read TilesetJsonLoader.cpp around line 1004 and reproduce the reported failure with a 3D Tiles content filename or URL containing a plus sign, using Cesium for Unity 1.16 on Unity 6.1. Done means that the tileset loads its tile content without the reported 404 caused by incorrect plus-sign handling.

Written by the indexing model from the issue text.