Zero initialize all pointer class and struct members

This prevents the pitfall of UB when checking if they have been
assigned something valid by comparing to nullptr.

modules/csg/csg_shape.h

@@ -368,7 +368,7 @@ private:
 	PathRotation path_rotation;
 	bool path_local;
 
-	Path3D *path;
+	Path3D *path = nullptr;
 
 	bool smooth_faces;
 	bool path_continuous_u;