Made sure that fDisplayMode is not modified if fAccSetDisplayMode failes,
as on my system fAccGetDisplayMode did return values that would crash
because of a virtual_width beeing 0.
Generally, this whole class is pretty broken, as the functions modify *some*
class member variables before eventually failing.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17352 a95241bf-73f2-0310-859d-f6bbb57e9c96