Fixed compiletime error that only occurred if ogl version was below 4.1

src/glow/objects/VertexArray.cc

@@ -229,7 +229,7 @@ void VertexArray::attachAttribute(const VertexArrayAttribute& va)
 #if GLOW_OPENGL_VERSION >= 41
         glVertexAttribLPointer(va.locationInVAO, a.size, a.type, stride, (const GLvoid*)(size_t)a.offset);
 #else
-        warning() << "Real 64bit precision double attributes are only supported in OpenGL 4.1+ " << to_string(this);
+        warning() << "Real 64bit precision double attributes are only supported in OpenGL 4.1+ " << to_string(getCurrentVAO()->vao);
 #endif
         break;
     }