overlay only works once

[stephenmathieson]

i've got a modal dialog which will be displayed any number of times (e.g. possibly more than once). seeing weird behaviour with the background "overlay" due to this line. any reason we don't just call overlay.remove() instead of setting it to null?

[pirxpilot]

Looks like a bug to me: hide calls hideOverlay, which hides/remove overlay and resets this._overlay - I think this line can be safely removed.