make JSSourceValue::baseValue const
make JSSourceValue::baseValue const

Change-Id: I2b40cc4fb20c4c3b6a7d779512acb2e24fff8bb1
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@digia.com>

villytiger/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,Distrotech/qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,villytiger/qbs,villytiger/qbs,qt-labs/qbs,villytiger/qbs,gatzka/qt-labs-qbs,villytiger/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,Distrotech/qbs,qt-labs/qbs