Loading BusStopPage causes segfault

[KrisztianOlah]

_Loading BusStopPage sometimes causes segfault._

Reproduce: rapidly open and close BusStopPage multiple times
Frequency: rare
Introduced in: 3b4a640
Details: When user navigates away from the page and header component(s) is/are not yet properly destroyed and user navigates back to BusStopPage creating new instance of header component.
QmlEngine reports multiple times: QQmlComponent: Cannot create new component instance before completing the previous
then: [W] unknown:-1 - file:///usr/lib/qt5/qml/Sailfish/Silica/private/HighlightImage.qml: RangeError: Maximum call stack size exceeded
and program terminates.