Add check for null pointer in EvaluatorScriptClass.
Add check for null pointer in EvaluatorScriptClass.

[Potential access to null pointer after the loop uncovered by clang
static analyzer.]

Change-Id: I8d46980c83d729963ffcb48c3dd5bc72262f4c29
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@theqtcompany.com>

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