Repair Special:Contributions and Special:RecentChanges

MultiDimArray::offsetSet was attempting to reference into a string
using array syntax.  In hhvm and php 5.5 this results in a null
assignment, but un 5.3.10 this is a fatal exception.

Additionally fixes FlowActions::hasValue which called MultiDimArray with
arguments leading to the bad reference.  Now catches the thrown
OutOfBounds exception and does BC checks similar to FlowActions::getValue

Bug: 71014
Change-Id: Ic0974b5057beabda4f72c13d5338e1b5e5eee21d