internal/postgres: initialize excluded state

Load the excluded table as soon as we create a DB, to
initialize in the in-memory state.

Change-Id: I1546566a1cf7c842b101ff8537f0433c8d170e32
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/262417
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
diff --git a/internal/postgres/postgres.go b/internal/postgres/postgres.go
index 78ab5f1..596067a 100644
--- a/internal/postgres/postgres.go
+++ b/internal/postgres/postgres.go
@@ -44,6 +44,7 @@
 			log.Errorf(context.Background(), "getting excluded prefixes: %v", err)
 		})
 	ctx, cancel := context.WithCancel(context.Background())
+	p.Poll(ctx) // Initialize the state.
 	p.Start(ctx, time.Minute)
 	return &DB{
 		db:                 db,