hugolib: Fix Pages reinitialization on rebuilds

Which had some unpredictable behaviour when using `.Pages` on home page etc. that had a content page.

Fixes #5833

hugolib/page__new.go

@@ -57,6 +57,7 @@ func newPageBase(metaProvider *pageMeta) (*pageState, error) {
 			RefProvider:             page.NopPage,
 			ShortcodeInfoProvider:   page.NopPage,
 			LanguageProvider:        s,
+			pagePages:               &pagePages{},
 
 			InternalDependencies: s,
 			init:                 lazy.New(),