[GL] fixed texture memory count in case of textures >=256MB (integer overflow)
[GL] fixed texture memory count in case of textures >=256MB (integer overflow)


Former-commit-id: a23c72060504418fae0c3df52b7238a301218bc3
vrvis/aardvark.rendering,vrvis/aardvark.rendering,vrvis/aardvark.rendering,vrvis/aardvark.rendering