mesh_library.h: Update header guard to reflect file name

scene/resources/mesh_library.h

@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifndef GRID_THEME_H
-#define GRID_THEME_H
+#ifndef MESH_LIBRARY_H
+#define MESH_LIBRARY_H
 
 #include "core/map.h"
 #include "core/resource.h"
@@ -96,4 +96,4 @@ public:
 	~MeshLibrary();
 };
 
-#endif // CUBE_GRID_THEME_H
+#endif // MESH_LIBRARY_H