Bugfix for 1118

Hide countdown as soon as race ends to prevent the drawGlobalTimer() method in race_gui from checking for failed challenges.

https://sourceforge.net/apps/trac/supertuxkart/ticket/1118

Signed-off-by: Sachith Hasaranga Seneviratne <sachith500@gmail.com>
Merge pull request #41 from sachith500/bug1118

Bugfix for 1118