Fix Store iteration bug

The previous code was only correctly iterating over a single block,
ignoring any others.

crates/fj-kernel/src/storage/blocks.rs

@@ -152,6 +152,7 @@ impl Index {
         self.object_index.0 += 1;
         if self.object_index.0 >= block.len() {
             self.block_index.0 += 1;
+            self.object_index.0 = 0;
         }
     }
 }

crates/fj-kernel/src/storage/store.rs

@@ -181,7 +181,7 @@ mod tests {
 
     #[test]
     fn insert_and_handle() {
-        let store = Store::new();
+        let store = Store::with_block_size(1);
 
         let object = 0;
         let handle = store.insert(object);
@@ -191,7 +191,7 @@ mod tests {
 
     #[test]
     fn insert_and_iter() {
-        let store = Store::new();
+        let store = Store::with_block_size(1);
 
         let a = store.insert(0);
         let b = store.insert(1);