Blender Git Loki

Fix T50904: Imprecise timeline frame selection using mouse

The changes introduced in rB3e628eefa9f55fac7b0faaec4fd4392c2de6b20e
made the non-subframe frame change behaviour less intuitive, by always
truncating downwards, instead of rounding to the nearest frame instead.
This made the UI a lot less forgiving of pointing precision errors
(for example, as a result of hand shake, or using a tablet on a highres scren)

This commit restores the old behaviour in this case only (subframe inspection
isn't affected by these changes)