Fix fd leak in rabbit_fifo

The handle_aux clause for `oldest_entry_timestamp` did not return
the updated Log structure and thus ends up leaking file descriptors
when this function is called and the segment isn't already open.

(cherry picked from commit 14da3a1)
(cherry picked from commit d0800d8)

Author: kjnilsson

deps/rabbit/src/rabbit_fifo.erl

@@ -1102,18 +1102,19 @@ handle_aux(_RaState, cast, eol, #?AUX{name = Name} = Aux, Log, _) ->
     ets:delete(rabbit_fifo_usage, Name),
     {no_reply, Aux, Log};
 handle_aux(_RaState, {call, _From}, oldest_entry_timestamp, Aux,
-           Log, #?MODULE{} = State) ->
-    Ts = case smallest_raft_index(State) of
-             %% if there are no entries, we return current timestamp
-             %% so that any previously obtained entries are considered older than this
-             undefined ->
-                 erlang:system_time(millisecond);
-             Idx when is_integer(Idx) ->
-                 %% TODO: make more defensive to avoid potential crash
-                 {{_, _, {_, Meta, _, _}}, _Log1} = ra_log:fetch(Idx, Log),
-                 #{ts := Timestamp} = Meta,
-                 Timestamp
-         end,
+           Log0, #?MODULE{} = State) ->
+    {Ts, Log} = case smallest_raft_index(State) of
+                    %% if there are no entries, we return current timestamp
+                    %% so that any previously obtained entries are considered
+                    %% older than this
+                    undefined ->
+                        {erlang:system_time(millisecond), Log0};
+                    Idx when is_integer(Idx) ->
+                        %% TODO: make more defensive to avoid potential crash
+                        {{_, _, {_, Meta, _, _}}, Log1} = ra_log:fetch(Idx, Log0),
+                        #{ts := Timestamp} = Meta,
+                        {Timestamp, Log1}
+                end,
     {reply, {ok, Ts}, Aux, Log};
 handle_aux(_RaState, {call, _From}, {peek, Pos}, Aux0,
            Log0, MacState) ->