Fix TextureData and cube map loading on 32-bit platforms

The 4 GB size checks for TextureData, compressed TextureData and cube
map faces cast quint32::max to qsizetype, which overflows to -1 on
32-bit platforms such as WebAssembly, so every texture was rejected:

    TextureData dimensions 1024x512x0 are not usable

This made ProceduralSkyTextureData unusable as a light probe. Compare
in 64 bits instead, as was already done for calculateDataSize().

Change-Id: Ia934c3ace2a05e85f4ce5fd3449907b92f3276f7
Reviewed-by: Christian Strømme <christian.stromme@qt.io>