Fix roompage sectionBanner visible check
change check to messageListView.sectionBannerItem != undefined
so that the command line isn't spammed with qrc:/RoomPage.qml:263:13: Unable to assign [undefined] to bool
change check to messageListView.sectionBannerItem != undefined
so that the command line isn't spammed with qrc:/RoomPage.qml:263:13: Unable to assign [undefined] to bool