allow challenge tasks to be displayed on challenge page - fixes https://github.com/HabitRPG/habitrpg/issues/4150
replace original challenge fix with negue's suggestion
Merge pull request #4151 from Alys/challengeFix-2014-10-16

allow challenge tasks to be displayed on challenge page - fixes https://github.com/HabitRPG/habitrpg/issues/4150