Ignore 'invisible' key presses

Don't generate key presses from 'invisible' keys (empty space
around 'q, a, backspace' on qwerty keyboard)

Open-webOS-DCO-1.0-Signed-off-by: Janne Kiiski <janne.kiiski@lge.com>

Change-Id: I46a84ae47d8e926d793f73565212701a00f43bb3