evas: Set thread name for preload

This can be useful during debugging.

src/lib/evas/cache/evas_cache_image.c

@@ -341,6 +341,8 @@ _evas_cache_image_async_heavy(void *data)
    int error;
    int pchannel;
 
+   eina_thread_name_set(eina_thread_self(), "Evas-preload");
+
    current = data;
 
    SLKL(current->lock);

src/lib/evas/include/evas_common_private.h

@@ -631,7 +631,7 @@ struct _Image_Entry
 
    Evas_Cache_Target     *targets;
    Evas_Preload_Pthread  *preload;
-   Eina_List             *tasks;
+   Eina_List             *tasks; // FIXME: Tasks are not used: always NULL func
 
    Image_Timestamp        tstamp;