Add initialization of JValue::asNumber() return value

:Release Notes:
Added initialization of return parameters in JValue::asNumber() methods

:Detailed Notes:

:Testing Performed:
Unit tests passed

:QA Notes:

:Issues Addressed:
[GF-37762] libpbnjson: JValue::asNumber<> does not initialize return
           value

Open-webOS-DCO-1.0-Signed-off-by: Mykola Kryvonos <mykola.kryvonos@lge.com>

Change-Id: Iea060c285b6ce38288cbcc4591a2e0d7750f02e8
Reviewed-on: https://g2g.palm.com/3607
Reviewed-by: Build Verification
Reviewed-by: Keith Derrick <keith.derrick@lge.com>
Tested-by: Keith Derrick <keith.derrick@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>