hdf5_msb

[svn-r17119] Bug fix #1513.  Reading an empty attribute caused seg fault.  The flag "initialized" in 
the attribute structure wan't set correctly.  It caused some confusion in H5A_read.  This
flag was actually redundant because the library can alwasy check if the data buffer is
present.  To fix it, I removed the "initialized" flag in the attribute structure and let
H5A_read check the data buffer.

Tested on jam, smirom, and linex.