The special case atan(y,0) of the built-in shader function atan(y,x)
returns different results on different devices. So this commit will add
checks when the atan(y,x) function is used in ParticlesMaterial to set
the direction of GPU Particles to make sure the desired values are
returned (act as atan2(y,x)).
(cherry picked from commit 3580ad6005)
6380943831