Fix worldSpace_linkAt not choosing closest Link

[joedight]

Fixes #45

[EdNutting]

Does this mean that if I click in completely empty space far away from any links, I might end up selecting something that is far away from where I clicked?

My instinct says a better solution is to have the search distance as a variable (instead of fixed 15) and scale it according to the current zoom level (with 15 being the base-case at the current default zoom).

[joedight]

I'm not entirely familiar with the codebase, but isn't this function in worldspace anyway, so we shouldn't need to worry about zoom level?
My intention here is to use 15 as the maximum distance (as it was before), but make sure that we always use a closer Link if it exists.

[EdNutting]

Ah I see, sorry I misunderstood the code earlier. This looks good to me then (sorry, long day syndrome :p )