Raise Z 5cm after stopping

Check if Z axis has been homed and, if so, raise Z at least 5cm after
stopping so that the steel sheet can be comfortably removed.

Firmware/ultralcd.cpp

@@ -6307,8 +6307,10 @@ void lcd_print_stop()
 
     lcd_cooldown(); //turns off heaters and fan; goes to status screen.
 
-    current_position[Z_AXIS] += 10; //lift Z.
-    plan_buffer_line_curposXYZE(manual_feedrate[Z_AXIS] / 60);
+    if (axis_known_position[Z_AXIS]) {
+        current_position[Z_AXIS] += 50; //lift Z.
+        plan_buffer_line_curposXYZE(manual_feedrate[Z_AXIS] / 60);
+    }
 
     if (axis_known_position[X_AXIS] && axis_known_position[Y_AXIS]) //if axis are homed, move to parked position.
     {