Crash after showing a Wayland Window on mesa llvmpipe

The issue could be reproduced on Ubuntu (16.04, 64bit) using the mesa llvmpipe based software renderer:
1. Start a Wayland compositor (e.g. weston or qwindow-compositor).
2. Launch the attached QML with:

LIBGL_ALWAYS_SOFTWARE=1 qmlscene window.qml -platform wayland

The crash occurs after the window is shown, hidden and shown again. It first appeared when running a Qt AS (appman) auto test on Ubuntu 16.04 in a virtual machine. The assumption is that hiding the window does not clean up all resources in QtWayland. It could however also be a bug in Mesa (this is the related bug report: https://bugs.freedesktop.org/show_bug.cgi?id=96953).