AP_Compass: only update last_update_ms on raw_field update if on calibration

libraries/AP_Compass/AP_Compass_Backend.cpp

@@ -45,15 +45,14 @@ void AP_Compass_Backend::rotate_field(Vector3f &mag, uint8_t instance)
 
 void AP_Compass_Backend::publish_raw_field(const Vector3f &mag, uint8_t instance)
 {
-    Compass::mag_state &state = _compass._state[Compass::StateIndex(instance)];
-
     // note that we do not set last_update_usec here as otherwise the
     // EKF and DCM would end up consuming compass data at the full
     // sensor rate. We want them to consume only the filtered fields
-    state.last_update_ms = AP_HAL::millis();
 #if COMPASS_CAL_ENABLED
     auto& cal = _compass._calibrator[_compass._get_priority(Compass::StateIndex(instance))];
     if (cal != nullptr) {
+        Compass::mag_state &state = _compass._state[Compass::StateIndex(instance)];
+        state.last_update_ms = AP_HAL::millis();
         cal->new_sample(mag);
     }
 #endif