R1:dbcd38aa881b

Fix the attempt of graceful alignment for Hovercards

Summary:
Refs T1048; Fixes T2902 - (Probably) fixes @vrana's issue. I managed
to repro it on Ubuntu FF (though on Windows with 1.0GHz/512MB it's
really worse...).

This revises the approach to the graceful degradation for
`too-far-to-the-screen-edge-edge-case`.

I noticed that `x` could become very negative, up to about ~`-170px`.
This is due to the //"already-on-the-left-side"// nature of object tags.
`50 - 200 - 20` = `negative`. Adding `100px` (node.