[VD] Don't show app if preload app is not ready

[VD] Don't show app if preload app is not ready

For ConnectTime app, when there is a video calling coming,
they will preload app, and when user connect the call,
they launch app, if the interval too short between perload and launch,
js still is not running when app is showing, but WRT has sent tizenvisibilitychange.
So app can't receive tizenvisibilitychange event.

Thus, if preload app is not ready, shouldn't show app.

Change-Id: I3838a1acf9e7f59d4d339e92c4417d13b1c6e363
Signed-off-by: zhaosy <shiyusy.zhao@samsung.com>