Fix a bug in hm2 encoder velocity estimation
Fix a bug in hm2 encoder velocity estimation

When the encoder changes direction by a single edge, we can not reliably
estimate velocity.  The encoder might be "balancing on an edge", leading
to potentially very small delta-T between edges, leading to misleadingly
large velocity estimation.  In this situation it's better to report
vel=0 and wait for more data to come in.

araisrobo/machinekit,yishinli/emc2,mhaberler/machinekit,araisrobo/machinekit,Cid427/machinekit,araisrobo/machinekit,araisrobo/machinekit,mhaberler/machinekit,EqAfrica/machinekit,cnc-club/linuxcnc,ianmcmahon/linuxcnc-mirror,Cid427/machinekit,jaguarcat79/ILC-with-LinuxCNC,bmwiedemann/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,EqAfrica/machinekit,Cid427/machinekit,bmwiedemann/linuxcnc-mirror,cdsteinkuehler/linuxcnc,jaguarcat79/ILC-with-LinuxCNC,unseenlaser/linuxcnc,Cid427/machinekit,jaguarcat79/ILC-with-LinuxCNC,araisrobo/linuxcnc,cnc-club/linuxcnc,kinsamanka/machinekit,yishinli/emc2,bobvanderlinden/machinekit,cnc-club/linuxcnc,araisrobo/machinekit,mhaberler/machinekit,cdsteinkuehler/linuxcnc,kinsamanka/machinekit,araisrobo/machinekit,ArcEye/machinekit-testing,narogon/linuxcnc,RunningLight/machinekit,Cid427/machinekit,RunningLight/machinekit,kinsamanka/machinekit,ianmcmahon/linuxcnc-mirror,araisrobo/linuxcnc,unseenlaser/machinekit,ikcalB/linuxcnc-mirror,cnc-club/linuxcnc,EqAfrica/machinekit,ArcEye/machinekit-testing,ianmcmahon/linuxcnc-mirror,ianmcmahon/linuxcnc-mirror,cdsteinkuehler/linuxcnc,bobvanderlinden/machinekit,unseenlaser/machinekit,jaguarcat79/ILC-with-LinuxCNC,RunningLight/machinekit,ikcalB/linuxcnc-mirror,araisrobo/linuxcnc,bmwiedemann/linuxcnc-mirror,mhaberler/machinekit,mhaberler/machinekit,RunningLight/machinekit,ArcEye/MK-Qt5,ArcEye/machinekit-testing,yishinli/emc2,Cid427/machinekit,unseenlaser/linuxcnc,ArcEye/MK-Qt5,ikcalB/linuxcnc-mirror,yishinli/emc2,unseenlaser/machinekit,strahlex/machinekit,araisrobo/machinekit,strahlex/machinekit,EqAfrica/machinekit,kinsamanka/machinekit,aschiffler/linuxcnc,EqAfrica/machinekit,cdsteinkuehler/MachineKit,RunningLight/machinekit,cdsteinkuehler/MachineKit,RunningLight/machinekit,cnc-club/linuxcnc,RunningLight/machinekit,araisrobo/linuxcnc,narogon/linuxcnc,cdsteinkuehler/MachineKit,ArcEye/MK-Qt5,ianmcmahon/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,strahlex/machinekit,bmwiedemann/linuxcnc-mirror,ArcEye/MK-Qt5,aschiffler/linuxcnc,unseenlaser/machinekit,araisrobo/machinekit,ArcEye/MK-Qt5,ArcEye/machinekit-testing,mhaberler/machinekit,strahlex/machinekit,bobvanderlinden/machinekit,mhaberler/machinekit,RunningLight/machinekit,ArcEye/machinekit-testing,aschiffler/linuxcnc,aschiffler/linuxcnc,EqAfrica/machinekit,kinsamanka/machinekit,unseenlaser/machinekit,cdsteinkuehler/MachineKit,strahlex/machinekit,Cid427/machinekit,narogon/linuxcnc,aschiffler/linuxcnc,narogon/linuxcnc,bmwiedemann/linuxcnc-mirror,ArcEye/machinekit-testing,EqAfrica/machinekit,bobvanderlinden/machinekit,Cid427/machinekit,ikcalB/linuxcnc-mirror,EqAfrica/machinekit,bobvanderlinden/machinekit,cdsteinkuehler/MachineKit,ArcEye/machinekit-testing,unseenlaser/machinekit,unseenlaser/machinekit,araisrobo/machinekit,ikcalB/linuxcnc-mirror,mhaberler/machinekit,cnc-club/linuxcnc,ArcEye/MK-Qt5,unseenlaser/linuxcnc,kinsamanka/machinekit,unseenlaser/machinekit,ianmcmahon/linuxcnc-mirror,cdsteinkuehler/MachineKit,ArcEye/MK-Qt5,kinsamanka/machinekit,ianmcmahon/linuxcnc-mirror,kinsamanka/machinekit,ikcalB/linuxcnc-mirror,cdsteinkuehler/linuxcnc,bobvanderlinden/machinekit,ikcalB/linuxcnc-mirror,jaguarcat79/ILC-with-LinuxCNC,cdsteinkuehler/linuxcnc,ArcEye/machinekit-testing,unseenlaser/linuxcnc,unseenlaser/linuxcnc,bobvanderlinden/machinekit,bobvanderlinden/machinekit,cnc-club/linuxcnc,cdsteinkuehler/linuxcnc,strahlex/machinekit,strahlex/machinekit,ArcEye/MK-Qt5,araisrobo/linuxcnc,narogon/linuxcnc