GM: Ignore 'DOWN' when the ring is going down

This is a follow-up commit to ed276656. This fixes the following crash:

=ERROR REPORT==== 18-Oct-2015::00:51:30 ===
** Generic server <0.966.0> terminating
** Last message in was {'DOWN',#Ref<0.0.3.4250>,process,<21148.716.0>,
                               shutdown}
** When Server state == {state,
                            ...
                            {true,{shutdown,ring_shutdown}}}
** Reason for termination ==
** {function_clause,[{orddict,fetch,
                              [{1,<0.966.0>},[]],
                              [{file,"orddict.erl"},{line,80}]},
                     {gm,check_neighbours,1,[{file,"src/gm.erl"},{line,1243}]},

Submitted by Alvaro Videla (@videlalvaro).
Fixes #368.

0 files changed, 0 insertions, 0 deletions