Airspeed calibration: Ensure that the calibration state is stored correctly

This is necessary due to sensors that are so accurate that they have no offset at all.

src/modules/commander/airspeed_calibration.cpp

@@ -175,6 +175,14 @@ int do_airspeed_calibration(orb_advert_t *mavlink_log_pub)
 			px4_close(fd_scale);
 		}
 
+		// Prevent a completely zero param
+		// since this is used to detect a missing calibration
+		// This value is numerically down in the noise and has
+		// no effect on the sensor performance.
+		if (fabsf(diff_pres_offset) < 0.00000001f) {
+			diff_pres_offset = 0.00000001f;
+		}
+
 		if (param_set(param_find("SENS_DPRES_OFF"), &(diff_pres_offset))) {
 			calibration_log_critical(mavlink_log_pub, CAL_ERROR_SET_PARAMS_MSG, 1);
 			goto error_return;