Fix autotests on Windows by re-adding weird conversion round-trip
Fix autotests on Windows by re-adding weird conversion round-trip

Commit dd57e76a43 removed a seemingly nonsensical QScriptValue ->
QString -> QScriptValue conversion, but without it, one autotest test
inexplicably fails on Windows (namely propertiesInExportItems, which
does not appear to be special in any way). Likely a QtScript issue.
Let's re-add the magic.

Change-Id: I83fbc62c2d5a1643ed8bba56e15531d2c42df3f9
Reviewed-by: Jake Petroules <2d627e1cecd5435752fa500bacbe05f7cc90c369@qt.io>

qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs