Automatic section pages are not replaced when using sites.complements #14540
Description
If a home page or section page in language A is not backed by a file, the "automatic" page is not replaced when complementing with another language.
integration test
// Issue 14540
func TestSiteComplementsOverrideAutomaticSectionPages(t *testing.T) {
t.Parallel()
files := `
-- hugo.toml --
disableKinds = ['rss', 'sitemap', 'taxonomy', 'term']
defaultContentLanguageInSubdir = true
[languages.en]
weight = 1
[languages.de]
weight = 2
[[module.mounts]]
source = 'content/en'
target = 'content'
[module.mounts.sites.matrix]
languages = ['en']
[module.mounts.sites.complements]
languages = ['de']
[[module.mounts]]
source = 'content/de'
target = 'content'
[module.mounts.sites.matrix]
languages = ['de']
-- layouts/home.html --
<ul>
{{ range $k, $_ := site.Pages -}}
<li>[{{ $k }}] <a href="{{ .RelPermalink }}">{{ .Title }}</a></li>
{{ end -}}
</ul>
-- layouts/page.html --
{{ .Title }}|
-- layouts/section.html --
{{ .Title }}|
-- content/en/_index.md --
---
title: home en
---
-- content/en/s1/_index.md --
---
title: s1 en
---
-- content/en/s1/p1.md --
---
title: p1 en
---
-- content/en/s2/_index.md --
---
title: s2 en
---
-- content/en/s2/p2.md --
---
title: p2 en
---
-- content/de/s1/p1.md --
---
title: p1 de
---
`
b := hugolib.Test(t, files)
b.AssertFileContent("public/en/index.html", `
<ul>
<li>[0] <a href="/en/">home en</a></li>
<li>[1] <a href="/en/s1/p1/">p1 en</a></li>
<li>[2] <a href="/en/s2/p2/">p2 en</a></li>
<li>[3] <a href="/en/s1/">s1 en</a></li>
<li>[4] <a href="/en/s2/">s2 en</a></li>
</ul>
`)
b.AssertFileContent("public/de/index.html", `
<ul>
<li>[0] <a href="/en/">home en</a></li>
<li>[1] <a href="/de/s1/p1/">p1 de</a></li>
<li>[2] <a href="/en/s2/p2/">p2 en</a></li>
<li>[3] <a href="/en/s1/">s1 en</a></li>
<li>[4] <a href="/en/s2/">s2 en</a></li>
</ul>
`)
}
// The second assertion above fails. Got:
// <ul>
// <li>[0] <a href="/de/"></a></li>
// <li>[1] <a href="/de/s1/p1/">p1 de</a></li>
// <li>[2] <a href="/en/s2/p2/">p2 en</a></li>
// <li>[3] <a href="/de/s1/">S1s</a></li>
// <li>[4] <a href="/en/s2/">s2 en</a></li>
// </ul>