Two changes in PageView's zoom combobox

- Removed useless document->supportsTiles() check in setupBaseActions()
setupBaseActions() is called only once, before a document is opened,
therefore supportsTiles() always returns false
- Show the 400% entry even when tiled rendering is not available, so
that the last entry always corresponds to the maximum allowed zoom
level (i.e. 1600% or 400% according to whether tiled rendering is
available or not)