tp: possible fix for div-by-zero in spindle-synced motion calculations
tp: possible fix for div-by-zero in spindle-synced motion calculations

Signed-off-by: Robert W. Ellenberg <7cf60555c449d119e88c087cd5eb42ff6272cb3e@gmail.com>

bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,ikcalB/linuxcnc-mirror