landdetector: exit landing state if manual.z is larger than threshold

src/modules/land_detector/MulticopterLandDetector.cpp

@@ -212,6 +212,7 @@ bool MulticopterLandDetector::_get_landed_state()
 		} else {
 			// Pilot wants to take off, assume no groundcontact anymore and therefore allow thrust
 			_ground_contact_hysteresis.set_state_and_update(false);
+			return false;
 		}
 	}