[rmodels] Improve default normal and tangent values (UploadMesh)

[Bigfoot71]

Description:

This PR updates the default normal and tangent values used when a mesh lacks corresponding buffers.

Changes:

• Default normal: Changed from (1, 1, 1) to (0, 0, 1) to ensure a properly normalized default normal, aligned with the standard convention of pointing out of the surface.
• Default tangent: Changed from (0, 0, 0, 0) to (1, 0, 0, 1) to provide a valid and reliable fallback for constructing the bitangent in shaders.

Benefits:

• Avoids potential problems when calculating the bitangent from a tangent that has a zero value.
• You can achieve optional normal mapping without requiring extra checks/shaders or conditional branches in shaders.

[raysan5]

@Bigfoot71 Looks good! Thanks for the improvement!