As explained in rB80d6421f2847, wm.h should not be used in snap3d_gizmo.c.

However, since the snap gizmo is only drawn when it is highlighed (that is,
when it "can be selected" which is when a snap point is found), its drawing
depends a lot on the test_select callback.

But gizmo values can be updated "manually", either by properties or by
utility functions. In this case, the snap gizmo must be drawn to indicate
the new snap point.

This patch proposes draw gizmo only when the eventstate located in
wm->winactive->eventstate has not changed.

So it doesn't matter if it's "selected" or not.