Fix missing header

src/graphics.cpp

@@ -19,6 +19,7 @@
 #include <config.hpp>
 #include <cv.hpp>
 #include <args.hpp>
+#include <error.hpp>
 
 GLuint shader;	//standard shader program used for all elements
 GLuint transUniform;	//location of the "transMatrix" transformation matrix uniform in the shader