elementary_tests.exe: Box Pack icons vanish after a while

[Coquinho]

Current behavior

1. Similar to #438 and #425 affter using Box Pack after a while it stops
   rendering new icons.
2. Other erros is that by Unpacking, on both native-window and master, generates:

ERR:elementary ../src/lib/elementary/efl_ui_focus_manager_calc.c:530 _register() Child 000040000082A01C is already registered in the graph (regular)

Expected behavior

1. Don't stop showing icons.
2. To don't throw errors while Unpacking.

Steps to reproduce

1. Run elementary_tests.exe
2. Open Box Pack app
3. Click on Pack at Start until no more icons appear (something like 24 times)
4. Click on Unpack All
5. Click some more times at Pack at Start and note some icons not showing its
   images

For the second error:

1. Run elementary_tests.exe
2. Open Box Pack app
3. Select an icon on the left bar
4. Click on Unpack
5. Your terminal now should have the erros disribed before.