Fix repeated emission of the finished() signal in JsCommandExecutor.
Fix repeated emission of the finished() signal in JsCommandExecutor.

This currently happens always if the command fails, resulting in an
assertion.

Change-Id: If3de00a2f0e7d89bd052a6ab74bf4237be82e913
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>

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