On the installation screen, focus was set first to the site title field, then moved to the password field. Autofocus should only ever be moved to the first field of a form, so that screen reader users don't miss important fields.
Fix by checking whether the site title field is present before setting password field focus.
Props zodiac1978, himanshupathak95, abcd95, joedolson.
Fixes#63281.
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