Kirigami master broken for Subsurface

[Dirk Hohndel]

Hey Marco,

339411cca69b in Kirigami breaks the edit overlay for Subsurface. Reverting
that commit makes things work again. It seems that reparenting the overlay
sheet to the page it finds messes things up for us...

Adding some debugging info I figured out that in our case the DiveDetails
page has no contentItem and therefore gets rejected as candidate... which
causes the loop to run all the way to the top of the object hierarchy and
the sheet being reparented to null.

Probably not what you wanted.

If I remove the check for the contentItem from the heuristic, things seem
to work.

/D