加载新字符集导致字体旧纹理被丢弃，TextMesh内纹理对象失效

[mouse0w0]

https://github.com/UnknownDomainGames/PanguEngine/blob/79d0ee15a8fcb22dd12c3e11cb8a2075f8ec724b/graphics/src/main/java/engine/graphics/font/TextMesh.java#L8-L13

TextMesh类中会存储文本网格的纹理。

https://github.com/UnknownDomainGames/PanguEngine/blob/79d0ee15a8fcb22dd12c3e11cb8a2075f8ec724b/graphics/src/main/java/engine/graphics/lwjgl/font/FontPlaneTexture.java#L72-L77

当FontPlaneTexture#dirty为true时（例如调用FontPlaneTexture#putBlock），会在下一渲染循环中调用FontPlaneTexture#bakeTexture，该方法将会dispose字体纹理对象，致使所引用该纹理的所有TextMesh对象无法正常渲染。