Condition LPE covariance to avoid blowing up in edge cases. (#5377)

Merging this as it is definitely more robust than what we have now.

src/modules/local_position_estimator/BlockLocalPositionEstimator.hpp

@@ -204,6 +204,7 @@ private:
 	// misc
 	float agl();
 	void correctionLogic(Vector<float, n_x> &dx);
+	void covPropagationLogic(Matrix<float, n_x, n_x> &dP);
 	void detectDistanceSensors();
 
 	// publications