Prevent double-click when moving the mouse.

SDL 2.0.9 introduced a 32-pixel leeway for double clicks to register, which makes it possible to trigger "select all units of the same type" behaviour while trying to select different units that are close by.

This effectively reverts that by setting the "hint" to 1.

Fixes #5920

Differential Revision: https://code.wildfiregames.com/D3420