EKF: Fix bug causing incorrect covariance initialisation

The covariance initialisation should not be performed before the quaternion states are initialised.

EKF/ekf_helper.cpp

@@ -1480,6 +1480,7 @@ Vector3f Ekf::calcRotVecVariances()
 }
 
 // initialise the quaternion covariances using rotation vector variances
+// do not call before quaternion states are initialised
 void Ekf::initialiseQuatCovariances(Vector3f &rot_vec_var)
 {
 	// calculate an equivalent rotation vector from the quaternion