Fix controlling_process fun in dispcount handler

@ferd hey, I found this bug in dlhttpc. It was causing an exception:
```erlang
10> dlhttpc:request("https://www.google.com, get, [], [], 10000, []).
=ERROR REPORT==== 17-Nov-2014::14:51:23 ===
** Generic server <0.110.0> terminating
** Last message in was {get,<0.144.0>}
** When Server state == {state,dlhttpc_handler,
                            {state,
                                {error,undefined},
                                false,
                                {"www.google.com",443,true,infinity,
                                 [binary,{packet,http},{active,false}]},
                                undefined},
                            {config,'dispcount_www.google.com443_ssl',10,ets,
                                57386,61483},
                            10,undefined}
** Reason for termination ==
** {error,function_clause}
```