The code assumed that a window gets resized when it enters/leaves the fullscreen
mode. This was needed because the code for resizing a window hides and shows the
titlebars.
However, it is possible for a window to enter/leave fullscreen mode without
getting resized, because it already has the correct geometry. In this case,
titlebars were not handled correctly.
This commit fixes that by forcing a resize to the current geometry when the
fullscreen flag is toggled.
Signed-off-by: Uli Schlachter <psychon@znc.in>