Summary:
Even if the XDG_RUNTIME_DIR is not set, KWayland should not crash
if methods are invoked which only make sense after the server was
started successfully. This was not yet the case for
Display::dispatchEvents.
Also the wl_display was not destroyed in the situation that creating
the socket failed.
Test Plan:
Test case added which simulates the situation of no
XDG_RUNTIME_DIR being set.
Reviewers: #plasma_on_wayland
Subscribers: plasma-devel
Tags: #plasma_on_wayland
Differential Revision: https://phabricator.kde.org/D2077