Various intermediate calculations would overflow inside both
`imb_save_openexr_float` and `imb_save_openexr_half`.
Additionally, use a raw array for the half conversion since `vector`
will perform an unnecessary zero-initialize on a large amount of memory.
Refer to: #135648
Pull Request: https://projects.blender.org/blender/blender/pulls/135678
5b26ae10a6