EKF: fix initialization of local position validity 2 (#820)

The `_deadreckon_time_exceeded` flag is used in
`local_position_is_valid()`. This means that
`_params.valid_timeout_max` after startup, in my observed case 5
seconds, the local position switche from valid to invalid and then after
a while back to valid again.

With this fix, the local position is flagged invalid from boot and gets validated after the first aiding event.

Co-authored-by: Julian Oes <julian@oes.ch>

EKF/ekf_helper.cpp

@@ -1215,8 +1215,8 @@ void Ekf::update_deadreckoning_status()
 		_time_last_aiding = _time_last_imu - _params.no_aid_timeout_max;
 	}
 
-	// report if we have been deadreckoning for too long
-	_deadreckon_time_exceeded = isTimedOut(_time_last_aiding, (uint64_t)_params.valid_timeout_max);
+	// report if we have been deadreckoning for too long, initial state is deadreckoning until aiding is present
+	_deadreckon_time_exceeded = (_time_last_aiding == 0) || isTimedOut(_time_last_aiding, (uint64_t)_params.valid_timeout_max);
 }
 
 // calculate the inverse rotation matrix from a quaternion rotation

test/test_EKF_fusionLogic.cpp

@@ -71,11 +71,9 @@ class EkfFusionLogicTest : public ::testing::Test {
 TEST_F(EkfFusionLogicTest, doNoFusion)
 {
 	// GIVEN: a tilt and heading aligned filter
-	// WHEN: having no aiding source EKF should not have a valid position estimate
-
-	// TODO: for the first 5 second it still has some valid local position
-	//       that needs to change
-	EXPECT_TRUE(_ekf->local_position_is_valid());
+	// WHEN: having no aiding source
+	// THEN: EKF should not have a valid position estimate
+	EXPECT_FALSE(_ekf->local_position_is_valid());
 
 	_sensor_simulator.runSeconds(4);