Fix checking code for string type min/maxLength

:Release Notes:
The minLength/maxLength checker of string type is already implemented.
But, pbnjson schema checker doesn't return fail.
Returning code is added.

:Detailed Notes:

:Testing Performed:

:QA Notes:

:Issues Addressed:

Open-webOS-DCO-1.0-Signed-off-by: Hyungjoon Lee <hyungjoon.lee@lge.com>

Change-Id: I46e29522470d9d7fff64285970f47b0dc3ee0857
Reviewed-on: https://g2g.palm.com/3006
Reviewed-by: Build Verification
Tested-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Mykola Kryvonos <mykola.kryvonos@lge.com>
Reviewed-by: Hyungjoon Lee <hyungjoon.lee@lge.com>
Tested-by: Hyungjoon Lee <hyungjoon.lee@lge.com>
Tested-by: Mykola Kryvonos <mykola.kryvonos@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>