bigarray: fix deserialization of float16 bigarrays

[gasche]

# let arr = Bigarray.(Array1.create float16 c_layout 10);;
val arr : (float, Bigarray.float16_elt, Bigarray.c_layout) Bigarray.Array1.t =
  <abstr>
# let raw = Marshal.to_string arr [];;
val raw : string = [...]
# Marshal.from_string raw 0;;
Exception: Failure "input_value: bad bigarray kind".

(I spotted the bug while reading the code of caml_ba_deserialize.)

[dra27]

I think there's a similar issue in the assertion in otherlibs/unix/mmap_ba.c?

[gasche]

I think there's a similar issue in the assertion in otherlibs/unix/mmap_ba.c?

Indeed, I also fixed that one and updated the PR. Thanks!

[dra27]

LGTM! Bug-fix is clearly correct. Although I expect we're not likely to add another type for another 10 years, the use of an UNIMPLEMENTED sentinel should ensure that that next addition is correct! 🙂