internal/relui: default to postgres as maintdb

In non-development environments, the default will be a database that is
the same as the username, which is not likely to exist.

For golang/go#47401

Change-Id: I2e4664f7917d1a63417cc1a19f800a043dff9d43
Reviewed-on: https://go-review.googlesource.com/c/build/+/363976
Trust: Alexander Rakoczy <[email protected]>
Run-TryBot: Alexander Rakoczy <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: toothrot

internal/relui/store.go

@@ -89,6 +89,9 @@ func MigrateDB(conn string, downUp bool) error {
 // with the name cfg.User will be used.
 func ConnectMaintenanceDB(ctx context.Context, cfg *pgx.ConnConfig, maintDB string) (*pgx.Conn, error) {
 	cfg = cfg.Copy()
+	if maintDB == "" {
+		maintDB = "postgres"
+	}
 	cfg.Database = maintDB
 	return pgx.ConnectConfig(ctx, cfg)
 }