AMP-lightbox with a nested iframe can't be opened multiple times

### Description

When nesting an AMP-iframe inside an AMP-lightbox, the lightbox render properly with the iframe when triggered.
However after I close the lightbox and re-open it - the lightbox gets a minimal height (i.e. it's not showing).

When I tried doing the same thing with version 0.1 of AMP-lightbox, the lightbox didn't load at all, and I got a message error "layoutcomplete race"

example: https://site.ampify.io/sites/amp-lightbox/index.html

### Reproduction Steps

1. Open https://site.ampify.io/sites/amp-lightbox/index.html
2. click to open the light box
3. close the lightbox
4. click to open it again

### Relevant Logs

_No response_

### Browser(s) Affected

Chrome

### OS(s) Affected

_No response_

### Device(s) Affected

_No response_

### AMP Version Affected

_No response_

Reproduce the behavior at https://site.ampify.io/sites/amp-lightbox/index.html by opening and closing the lightbox, then opening it again; compare this with AMP-lightbox 0.1 and the reported "layoutcomplete race" error. Trace the AMP-lightbox and nested AMP-iframe lifecycle, and consider the issue done when repeated openings render the iframe at the expected height without that error.

Written by the indexing model from the issue text.