Conditionally include apriltag header

Author: g3force

src/app/plugins/plugin_visualize.cpp

@@ -19,10 +19,13 @@
 */
 //========================================================================
 #include "plugin_visualize.h"
-#include <apriltag.h>
 #include <opencv2/opencv.hpp>
 #include <sobel.h>
 
+#ifdef APRILTAG
+#include <apriltag.h>
+#endif
+
 namespace {
 typedef CameraParameters::AdditionalCalibrationInformation AddnlCalibInfo;
 } // namespace