[rmodels] Read uninitialized values in `GenMeshTangents()`

[listeria]

This commit (c4a51a3) will skip the last iteration if mesh->vertexCount % 3 == 0 (I suppose this is the normal case), which results in the last values for tan1 and tan2 being uninitialized. In any case this reads uninitialized memory from the end of tan1 and tan2 in the next loop regardless of the value of mesh->vertexCount. Did you mean to use i <= mesh->vertexCount - 3? Maybe a better option would be to assert that mesh->vertexCount % 3 == 0 and keep the old loop, since otherwise the last 1 or 2 values from tan1 and tan2 will always be uninitialized, which is probably not what you want.

\cc @sgalindo

[Ray]

@ListeriaM Thanks for the further review, I didn't notice it...