Fix for listUserWords

:Release Notes:
Add verification for parameters values

:Detailed Notes:

:Testing Performed:
tested on build

:QA Notes:
get number of user words:
  luna-send -n 1 -f palm://com.palm.smartKey/numUserWords '{}'
list user words:
  luna-send -n 1 -f palm://com.palm.smartKey/listUserWords '{ "offset":0, "limit":2}'

:Issues Addressed:
[GF-10663] com.palm.smartKey:listUserWords - returns True for invalid offset and limit

Open-webOS-DCO-1.0-Signed-off-by: Igor Kuksyuk <ikuksyuk@luxoft.com>

Change-Id: I44fcf9bb73b82bd6ad86f7b1662e1a53ead62ae9
Reviewed-on: https://g2g.palm.com/3552
Reviewed-by: Igor Kuksyuk <ikuksyuk@luxoft.com>
Tested-by: Igor Kuksyuk <ikuksyuk@luxoft.com>
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>