Input::mouseDelta jumps when mouse moves for the first time

[RiscadoA]

Problem

The mouseDelta input method returns the movement of the mouse in the last frame. The first time the mouse moves though, it gives a huge delta, which makes FPS cameras and stuff like that buggy - the game dev must add a bool checking whether it is the first movement or not, and ignore it if it is.

Solution

We should keep a flag on whether the mouse has moved before. If it hasn't, then the first mouse delta is discarded automatically and the method should return (0, 0).