fix(NcModal): fix focus-trap fallback

[skjnldsv]

Fix #4265

Sometimes the content is empty or not ready yet.

fallbackFocus {HTMLElement | SVGElement | string | () => HTMLElement | SVGElement | string}: By default, an error will be thrown if the focus trap contains no elements in its tab order. With this option you can specify a fallback element to programmatically receive focus if no other tabbable elements are found. For example, you may want a popover's

to receive focus if the popover's content includes no tabbable elements. Make sure the fallback element has a negative tabindex so it can be programmatically focused. The option value can be a DOM node, a selector string (which will be passed to document.querySelector() to find the DOM node), or a function that returns any of these.

[skjnldsv]

/backport to stable7

[susnux]

@skjnldsv something is wrong with the package lock: 20,786 additions, 2 deletions
Are you using the correct node version? As the lockfile version is also downgraded from 3 to 2 with this update.

[skjnldsv]

@skjnldsv something is wrong with the package lock: 20,786 additions, 2 deletions Are you using the correct node version? As the lockfile version is also downgraded from 3 to 2 with this update.

Nice catch, haven't updated node on this terminal since the LTS merge

[skjnldsv]

Preview looks good, and content still focusable 👍

[backportbot-nextcloud]

The backport to stable7 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable7
git pull origin stable7

# Create the new backport branch
git checkout -b fix/foo-stable7

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable7

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[skjnldsv]

#4270