Initialize a variable so it can correctly be dealt with at shutdown - fixes trac:1312

This commit was SVN r18505.

The following Trac tickets were found above:
  Ticket 1312 --> https://svn.open-mpi.org/trac/ompi/ticket/1312

orte/mca/odls/base/odls_base_default_fns.c

@@ -68,7 +68,7 @@
 #include "orte/mca/odls/base/odls_private.h"
 
 static int8_t *app_idx;
-static char **slot_str;
+static char **slot_str=NULL;
 
 /* IT IS CRITICAL THAT ANY CHANGE IN THE ORDER OF THE INFO PACKED IN
  * THIS FUNCTION BE REFLECTED IN THE CONSTRUCT_CHILD_LIST PARSER BELOW