fix rval

Author: lukebakken

src/vm_memory_monitor.erl

@@ -188,7 +188,7 @@ get_system_process_resident_memory({win32,_OSname}) ->
     % Note: 3.6.12 shipped with code that used wmic.exe to get the
     % WorkingSetSize value for the running erl.exe process.
     % See rabbitmq/rabbitmq-server#1343 for details
-    erlang:memory(total);
+    {ok, erlang:memory(total)};
 
 get_system_process_resident_memory({unix, sunos}) ->
     get_ps_memory();