hugolib: Re-work "fast render" logic in the new flow

Note that this fixes some "live reload" issues recently introduced in non-released code.

Closes #5811
See #5784

hugolib/hugo_sites.go

@@ -569,7 +569,6 @@ func (cfg *BuildCfg) shouldRender(p *pageState) bool {
 		return false
 	}
 	if p.forceRender {
-		p.forceRender = false
 		return true
 	}
 
@@ -577,6 +576,10 @@ func (cfg *BuildCfg) shouldRender(p *pageState) bool {
 		return true
 	}
 
+	if cfg.RecentlyVisited[p.RelPermalink()] {
+		return true
+	}
+
 	if cfg.whatChanged != nil && !p.File().IsZero() {
 		return cfg.whatChanged.files[p.File().Filename()]
 	}