Fix unsetting the selected page for an event version
Fix unsetting the selected page for an event version

We were calling `$version->setPageObject(0)` when this method only accepts instances of `Page`. Instead let's call `$version->setPageID(0)` to unset.
a3020/concrete5,biplobice/concrete5,jaromirdalecky/concrete5,mlocati/concrete5,deek87/concrete5,concrete5/concrete5,jaromirdalecky/concrete5,biplobice/concrete5,biplobice/concrete5,mlocati/concrete5,haeflimi/concrete5,olsgreen/concrete5,MrKarlDilkington/concrete5,haeflimi/concrete5,triplei/concrete5-8,concrete5/concrete5,mlocati/concrete5,deek87/concrete5,haeflimi/concrete5,deek87/concrete5,concrete5/concrete5,mainio/concrete5,hissy/concrete5,a3020/concrete5,rikzuiderlicht/concrete5,rikzuiderlicht/concrete5,rikzuiderlicht/concrete5,olsgreen/concrete5,MrKarlDilkington/concrete5,haeflimi/concrete5,deek87/concrete5,mainio/concrete5,MrKarlDilkington/concrete5,olsgreen/concrete5,jaromirdalecky/concrete5,hissy/concrete5,hissy/concrete5,jaromirdalecky/concrete5,concrete5/concrete5,mlocati/concrete5,triplei/concrete5-8,hissy/concrete5,biplobice/concrete5,triplei/concrete5-8,mainio/concrete5