hdf5_ep

[svn-r18063] Fix bug in links.c which occurs when zlib is disabled.  This was fixed in the
trunk in r17751, but was not ported to 1.8 because that feature (compress group
fheap) had not beed added to 1.8 yet.  This fix should have been ported to the
cgfh branch at the time, but it was overlooked.

Tested: Fedora (too small for commit test)