Don't move the map if the image is overlay already visible at the current location

[Glodenox]

It is not needed to move and zoom the map if the image overlay is already visible in the viewport whenever the overlay is activated.

Consider adding a crosshairs button as well that only shows up whenever people hover over the image entry. Perhaps just hide all action buttons until that happens. Might be a bit impractical on mobile devices though (also listen to :activeevent?)