a few areas that use ED_view3d_win_to_segment_clip() didnt take into account the case where the segment was filly clipped, some callers even needed the segment not to be clipped.
- added ED_view3d_win_to_segment()
- ED_view3d_win_to_segment_clip() now returns FALSE if the segment is totally clipped, but the start/ends of the line are not zero'd as they were before.