Panic in drop leads to a double drop on spawning a new entity

From https://github.com/bevyengine/bevy/issues/2597#issuecomment-892066719

I think this happens due to `Table::allocate` increasing the column length before the data is actually written.

I also have a test for this, based on https://github.com/bevyengine/bevy/pull/2848

```rust
#[test]
fn panic_in_despawn_followed_by_insert() {
let helper = DropTestHelper::new();

let res = panic::catch_unwind(|| {
let mut world = World::new();

let e1 = world.spawn(helper.make_component(true, 0)).id();

let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
world.despawn(e1);
}));

world.spawn(helper.make_component(true, 1));

println!("Done inserting! Dropping world...");
});

let drop_log = helper.finish(res);

assert_eq!(
&*drop_log,
[
DropLogItem::Create(0),
DropLogItem::Drop(0),
DropLogItem::Create(1),
DropLogItem::Drop(1)
]
);
}
```