evas: Fix shutdown of async cmd cache

The incomplete reset (array to NULL but max not reset) triggers errors
in evas_thread_queue_append() where eina_inarray_grow() returns NULL.

This shows up in:
   CK_FORK=no elm_suite

@fix

src/lib/evas/canvas/evas_async_events.c

@@ -158,6 +158,7 @@ evas_async_events_shutdown(void)
 
    free(async_queue_cache);
    async_queue_cache = NULL;
+   async_queue_cache_max = 0;
 
    eina_spinlock_free(&async_lock);
    eina_inarray_flush(&async_queue);

src/lib/evas/common/evas_thread_render.c

@@ -270,6 +270,7 @@ timeout_shutdown:
 
    free(evas_thread_queue_cache);
    evas_thread_queue_cache = NULL;
+   evas_thread_queue_cache_max = 0;
    eina_inarray_flush(&evas_thread_queue);
 
    eina_threads_shutdown();