[MODELS] Fix crash with some GLTF models

[JeffM2501]

When a buffer is read using cgltf_load_buffer_base64, the data is a raw void*, so we can't call cgltf_free. cgltf_free assumes the data is a cgltf_data structure and will try to free the various buffers in that structure.
This causes a crash with some files (attached)
house.zip

This PR calls a normal free for the data, so it's properly deallocated so it won't crash.
I could not find a pure free method in cgltf, so I just called raylib's free since it looks like that is what is installed for cgltf's allocators anyway.

[raysan5]

@JeffM2501 This issue could be a bit tricky...

data should be freed by the same allocation library used to allocate it. In this case, cgltf calls cgltf_default_alloc() that calls CGLTF_MALLOC that rmodels map to RL_CALLOC, so, calling MemFree() that calls RL_FREE end-up using the right allocators pair... BUT there could be some situation, like user setting up custom allocation/free pairs on raylib, that could let to undesired effects.

Clearly cgltf_free() can not be used to unload data. Ideally, cgltf_load_buffer_base64() should provide a unload function equivalent... In the meantime, I'm merging this fix.

Related to jkuhlmann/cgltf#200

[JeffM2501]

Yeah, I was hoping they exposed a proper free, but I didn't see one, so yeah it's tricky.