Qt wayland client' main thread blocks if it is not visible on the compositor

The same issue reported by QTBUG-74715 for Qt5.12 has been observed with Qt5.6.3.
The original patch (https://codereview.qt-project.org/#/c/251380/5/) can not be applied.

Problem description

QtWaylandClient blocks the main thread when it is not visible in the compositor window.
The thread continues if the client application is brought to foreground (i.e. visible). It is suspected that the wayland client waits for an event from the wayland compositor.

The issue causing the client to block is reproducible in two cases:

1. When a client is connected,  its wayland surface is attached to a surfaceItem (with visible: false)
2. When a client is connected, its wayland surface is attached to a surfaceItem (with visible: true). After that, the surfaceItem is destroyed.