control: do not crash on unavaible HAproxy socket

lib/ha_handler/control.ex

@@ -173,8 +173,13 @@ defmodule HAHandler.Control do
   def handle_info(:sync, state) do
     Logger.debug("Executing control logic.")
 
+    case HAProxy.get_stats() do
+      %{} ->
         process_pgsql()
         process_drbd()
+      {:error, err} ->
+        Logger.error("Unable to fetch HAProxy state (#{inspect(err)}( - skipping control loop.")
+    end
 
     # Schedule next round.
     Process.send_after(self(), :sync, @refresh)