[TIMOB-10017] added null check for windowActivity

[salachi]

TIMOB-10017 - Made sure that windowActivity is not null before calling setBackgroundDrawable.
Test case is running without crash after the change

[pingwang2011]

FR failed
Ran the test case in https://jira.appcelerator.org/browse/TIMOB-10017 . Click the button to open the second window and then click the "back" button. Click the button to open the second window again. Scroll the table view and you can see two table views overlap together. Seems like when clicking the "back" button the second window is not closed correctly and the child views are not released at all.
BTW, please add "TIMOB-xxxx" in the commit message so it's easy to find out why we do such change later.

[salachi]

The window doesn't get closed because the test case code keep on adding table to the window. This is a test case error. It needs to trap the android back event and cleanup the table that is added. The fix should fix the crash.

[pingwang2011]

By clicking "back" button, the window activity should finish and the window should close and all the views in the window should be released. I attached another test case in JIRA which calls close() explicitly and you can see the same issue as I described above. I think the root of the crash is window is not closed correctly.

[pingwang2011]

BTW, after clicking "open" and "close" buttons a few times, I can see some memory leak through DDMS which also means the window is not closed correctly and some views are not released.

[salachi]

I will take a look at this.

[ayeung]

Closing due to inactivity.