gscreen -fix error related to keyboard jogging and limit switch

If keyboard jogging and one hits a limit switch, you would get
an endless amount of error messages.
Thanks Ivan the Red on forum for testing fixes

Author: c-morley

src/emc/usr_intf/gscreen/emc_interface.py

@@ -139,6 +139,7 @@ def set_motion_mode(self):
 
         def continuous_jog_velocity(self, velocity,angular=None):
                 if self.masked: return
+                if self.is_machine_off(): return
                 self.set_motion_mode()
                 if velocity == None:
                     rate = self.angular_jog_velocity = angular / 60.0
@@ -151,6 +152,7 @@ def continuous_jog_velocity(self, velocity,angular=None):
 
         def continuous_jog(self, axis, direction):
                 if self.masked: return
+                if self.is_machine_off(): return
                 self.set_motion_mode()
                 if direction == 0:
                         self.isjogging[axis] = 0
@@ -170,6 +172,7 @@ def stop_jog(self, axis):
 
         def incremental_jog(self, axis, direction, distance):
                 if self.masked: return
+                if self.is_machine_off(): return
                 self.set_motion_mode()
                 self.isjogging[axis] = direction
                 if axis in (3,4,5):
@@ -292,6 +295,15 @@ def get_mode(self):
             self.emcstat.poll()
             return self.emcstat.task_mode
 
+        def is_machine_off(self):
+            self.emcstat.poll()
+            state = self.emcstat.task_state != self.emc.STATE_ON
+            if state:
+                # kill any jogging state
+                for i in range(0,len(self.isjogging)):
+                    self.isjogging[i] = 0
+            return state
+
 class emc_status:
         def __init__(self, data, emc):
             self.data = data