Added UBSAN complaint fix to rLoadTexture #1891

[Codom]

I managed to trigger the ubsan by simply calling LoadRenderTexture(1280, 720); from zig. Looking at recent PR's and issues it seems like this issue has already been mitigated elsewhere, but still exists in the codepath for LoadRenderTexture.

All I did was apply a similar fix (as seen in 30a9a24) for #1891 to the rLoadTextures function. This seems to fix the issue.

[raysan5]

Please note that there is an error, mipOffset += mipSize; is called later in the loop, so dataPtr += mipSize should be added.

[Codom]

Ah, missed that. I just recompute the offset from data on every iteration, dataPtr = (unsigned char*)data + mipOffset which is more in line with the previous version.

[raysan5]

@Codom did you add the chnage? I can't see it.

[Codom]

It should be here: f0e7511
Apologies for any confusion.

[raysan5]

@Codom I'm merging it but I'm reviewing this implementation, I'll take the variable definition out of the loop and also the conditional check.