sensors app: Always set a valid rotation, even if sensor is unconfigured

src/modules/sensors/sensors.cpp

@@ -1480,9 +1480,16 @@ Sensors::parameter_update_poll(bool forced)
 			int fd = open(str, 0);
 
 			if (fd < 0) {
+				/* the driver is not running, abort */
 				continue;
 			}
 
+			/* set a valid default rotation (same as board).
+			 * if the mag is configured, this might be replaced
+			 * in the section below.
+			 */
+			_mag_rotation[s] = _board_rotation;
+
 			bool config_ok = false;
 
 			/* run through all stored calibrations */