Review fix. dialog.close() clears `open` at once but queues the close
event that empties the dialog. A conflict read that resumed in between
still found the old form connected and reopened the dialog, and the
queued event then emptied it: an open modal with nothing in it. The
check is now the dialog's own `open` state and that it still holds the
form. A browser test closes the dialog and releases the read's body in
one task; it fails on the previous commit.
jason.woltje
95ee19cc71