refactor(cursor): make Cursor::new pub(crate) and check for nullptr o…

…n `World::cursor_id`

flecs_ecs/src/addons/meta/cursor.rs

@@ -10,7 +10,7 @@ pub struct Cursor<'a> {
 impl<'a> Cursor<'a> {
     /// Creates a new cursor instance
     #[allow(clippy::not_unsafe_ptr_arg_deref)]
-    pub fn new(
+    pub(crate) fn new(
         world: impl WorldProvider<'a>,
         type_id: impl Into<Entity>,
         ptr: *mut std::ffi::c_void,

flecs_ecs/src/addons/meta/mod.rs

@@ -75,6 +75,10 @@ impl World {
     ///
     /// * C++ API: `world::cursor`
     pub fn cursor_id(&self, type_id: impl Into<Entity>, ptr: *mut c_void) -> Cursor {
+        if ptr.is_null() {
+            panic!("ptr is null");
+        }
+
         Cursor::new(self, type_id, ptr)
     }