Merge pull request #4485 from apache/couch_index_crashes

catch and log any error from mem3:local_shards
diff --git a/src/couch_index/src/couch_index_server.erl b/src/couch_index/src/couch_index_server.erl
index 2e368bf..c344002 100644
--- a/src/couch_index/src/couch_index_server.erl
+++ b/src/couch_index/src/couch_index_server.erl
@@ -312,7 +312,11 @@
         try
             mem3:local_shards(mem3:dbname(DbName))
         catch
-            error:database_does_not_exist ->
+            Class:Msg ->
+                couch_log:warning(
+                    "~p got ~p:~p when fetching local shards for ~p",
+                    [?MODULE, Class, Msg, DbName]
+                ),
                 []
         end,
     DbShards = [mem3:name(Sh) || Sh <- LocalShards],