Allow preloadparams for Special:MyPage

The param was added with If02cf4b3dba9f9d22a956d8bfff224677cbce00d
This allows using it along with the already allowed preload=
The preloadparams is a array param, which needs support in
getRedirectQuery

Change-Id: Ib4f369a39d989c7038b735b862883641aa3aa354
Merge "Allow preloadparams for Special:MyPage"