Fix a bug spotted by IBM's BEAM checker in VG_(describe_IP).
In the non-XML part buf_dirname was read without observing the
know_dirinfo guard. Now fixed. Initialise buf_dirname nevertheless.
Also remove a dead assignment.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14707 a5019735-40e9-0310-863c-91ae7b9d1cf9