[FIX] trackers: $filterfield is usually an array so casting it to an int wipes the value (r47946 regression), also $ev is now initialised properly to check for empty instead of isset so filtervalue gets searched for properly (should fix wish4789, thanks Xavi)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@48070 b456876b-0849-0410-b77d-98878d47e9d5