Panic when adding a node

[simonchatts]

Describe the bug
Sometimes, when a dom node is dynamically added to an existing tree, one can hit the panic in utils::render::reconcile_fragments.

To Reproduce
Render the component below, using release 0.6.0:

use sycamore::prelude::*;

#[component(ReproBug<G>)]
pub fn repro_bug() -> Template<G> {
    let mid_drag = Signal::new(false);

    let on_drag_enter = cloned!((mid_drag) => move |_|
        mid_drag.set(true)
    );

    template! {
        div(style="background:red; color:white;margin: 10px; width: 120px;",
            draggable="true") { "↓ Drag me! ↓"}

        div(style="background:blue; color:white; margin: 10px; width: 120px;",
            on:dragenter=on_drag_enter) { "→ Onto here! ←"}

        (if *mid_drag.get() {
            template! { p() { "Dragging!" } }
        } else {
            template! {}
        })
    }
}

If I drag the red div onto the blue one. I get the panic:

panicked at 'node 2 in existing nodes Vec is not a child of parent. node = DomNode(
    "<p>Dragging!</p>",
)', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/sycamore-0.6.0/src/utils/render.rs:240:17

Expected behavior
No panic, and the "Dragging!" p node should be added to the dom tree.

Environment

• Sycamore: 0.6.0
• Browser: tested on Chrome, Firefox, and Safari
• OS: MacOS