monitor: Fix file_completion() to check for stat() failure
stat() can fail for a file name just read with readdir(). Easiest way
to trigger is a dangling symbolic link --- look ma, no race! When it
fails, file_completion() uses sb.st_mode uninitialized. If the
directory bit happens to be set, it appends a "/" to the completed
name.
Signed-off-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>