Stop back key android from quitting application WHILE the scene is loading?

Hello. I’m using Unity 4.3.4.

If I press back key on android phone while the scene is loading, the entire application quits.
I have already known the code below.

 if (Input.GetKeyDown(KeyCode.Escape))    

But this solution only work if scene is loading completely.
I have already add DonDestroyOnLoad to script, but nothing changes.

If anyone find out solution, pls let me know. Thank in advance

Rather than doing: return; try: end;