FileDialog only return selected fileurl correctly at the first, but return null fileurl at the second times

In  the imageviewer-mobile sample of qmlbook(http://qmlbook.github.io/assets/ch06-controls-assets.tgz, when the first time open the FileDialog and select an image file, the image file can show in Image item. But the second time open  the FileDialog and select another image file, none is show in Image item for filedialog return null fileurl in its onAccepted function. 

The bug is only exists in Qt for Android 5.15 but not exists in 5.14.2.