Revert "Revert "nshlib: fix possible out of bounds array access""

This reverts commit fe4b44e3ff.

nshlib/nsh_fsutils.c

@@ -513,7 +513,6 @@ FAR char *nsh_getdirpath(FAR struct nsh_vtbl_s *vtbl,
       snprintf(vtbl->iobuffer, IOBUFFERSIZE, "%s/%s", dirpath, path);
     }
 
-  vtbl->iobuffer[PATH_MAX] = '\0';
   return strdup(vtbl->iobuffer);
 }
 #endif