Merge pull request #50 from sletta/master

[compositor] Prevent crash when extended surface is destroyed.
[compositor] Set the content orientation of the extended window to the QWindow's content orientation when the QWaylandWindow is created
Merge pull request #51 from Vesuri/contentorientation

[compositor] Set the content orientation of the extended window to the QWindow's content orientation when the QWaylandWindow is created
[compositor] Initialize 'm_visibility' member variable
[compositor] Avoid potential crash in compositor.

If we called disown on a buffer after it got destroyed we would
touch the m_buffer handle which was then invalid which would
crash.