AppletQuickItem: Fix weird format of error messages
The previous message was containing a user-visible string and was missing context, for example: kf.plasma.quick: QJsonValue(string, "Printers") kf.plasma.quick: QJsonValue(array, QJsonArray([".../org.kde.plasma.printmanager/contents/ui/main.qml:56:34: Type FullRepresentation unavailable","... : module "QtQuick.Controls" version 1.3 is not installed"]))
Now, one gets: kf.plasma.quick: error when loading applet "org.kde.plasma.printmanager" QList("... Type FullRepresentation unavailable", "...: module "QtQuick.Controls" version 1.3 is not installed")