okular active: Do not position pages on non-exact pixel boundaries

Round page position to the nearest pixel, because at some zoom levels on
my laptop okular active tries to draw page pixmaps at non-exact pixel
boundaries, resulting in almost unreadable text.

CCMAIL: notmart@gmail.com
REVIEW: 111782

active/app/package/contents/ui/FullScreenDelegate.qml

@@ -159,9 +159,10 @@ MouseEventListener {
                 id: mainPage
                 document: documentItem
                 flickable: mainFlickable
-                anchors.centerIn: parent
                 property real ratio: implicitWidth / implicitHeight
 
+                x: Math.round((parent.width - width) / 2)
+                y: Math.round((parent.height - height) / 2)
                 width: implicitWidth
                 height: implicitHeight
             }