SDK's LightSource shadowmask tex not working on MacOS for raw textures

[pravusjif]

For the texture used for the shadowmask of the LightSource SDK component, TextureFuse is failing to convert textures in some scenarios (e.g. using the test-scene from this other issue...) and the texture ends up being null, making shadowmask textures not work for Local Scene Development in MacOS.

Running in MacOS, in this test scene: https://github.com/decentraland-scenes/light-memory-leak-test instead of getting the expected shadowmask behaviour:

Lightsource-2.mp4

the shadowmask doesn't work at all:

Lightsource-1.mp4

We have to implement a fallback to use the uncompressed texture when TextureFuse fails.