Update the default setting for the memb_addr array when use passes NULL to equally divide all the address space between all the members.
Before there was one chunk of the address space not being used.

tested h5committest, and multi vfd make check on jam.



git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25661 dab4d1a6-ed17-0410-a064-d1ae371a2980