Set preferredWidth instead of using fillWidth in PlaceholderMessage
This causes recursive re-arranges in certain situations on Qt5. Sibling MR to frameworks/kirigami!1034 (closed) which is only needed for Qt5/KF5.
This causes recursive re-arranges in certain situations on Qt5. Sibling MR to frameworks/kirigami!1034 (closed) which is only needed for Qt5/KF5.