perlmods: Update Starlink::HDSPACK for HDF5

Turns out that HDF5 is sensitive about the opening order of
files in that you can't open a file readonly and then expect
to be able to open the file again read/write.
hds-v5: Improve efficiency of datVec then datSlice

Also fix datUnmap and attempt to catch HDF5 CANTOPENFILE
error.