desktop-shell: Check height instead of checking width a second time

Fix an apparent copy and paste error in resize code. I'm not sure anything sets the relevant callback that would lead to height being different than width, so there's no easy way to demonstrate a bug, but this change appears to rectify the intent of the code.

Reported-by: Hideyuki Nagase hideyukn@microsoft.com Signed-off-by: Derek Foreman derek.foreman@collabora.com