ecore_thread: null out the struct before returning it

it can contain old callback values which are not overwritten in every
case. This just ensures that in both cases, empty trasher or none empty
trasher, are returning the same state of the struct.

src/lib/ecore/ecore_thread.c

@@ -537,6 +537,10 @@ _ecore_thread_worker_new(void)
        result = calloc(1, sizeof(Ecore_Pthread_Worker));
        _ecore_thread_worker_count++;
      }
+   else
+     {
+        memset(result, 0,  sizeof(Ecore_Pthread_Worker));
+     }
 
    SLKI(result->cancel_mutex);
    LKI(result->mutex);