Copter: log error if circle does not initialise correctly

ArduCopter/control_auto.cpp

@@ -456,6 +456,7 @@ void Copter::auto_circle_movetoedge_start(const Location_Class &circle_center, f
     if (!circle_center.get_vector_from_origin_NEU(circle_center_neu)) {
         // default to current position and log error
         circle_center_neu = inertial_nav.get_position();
+        Log_Write_Error(ERROR_SUBSYSTEM_NAVIGATION, ERROR_CODE_FAILED_CIRCLE_INIT);
     }
     circle_nav.set_center(circle_center_neu);
 

ArduCopter/defines.h

@@ -407,6 +407,7 @@ enum ThrowModeState {
 // subsystem specific error codes -- navigation
 #define ERROR_CODE_FAILED_TO_SET_DESTINATION    2
 #define ERROR_CODE_RESTARTED_RTL            3
+#define ERROR_CODE_FAILED_CIRCLE_INIT       4
 
 // parachute failed to deploy because of low altitude or landed
 #define ERROR_CODE_PARACHUTE_TOO_LOW        2