store: Close Rows in hasColumn.

Not closing the Rows will cause SQLite3 to lock the database and block all
other clients.

store/sqlutil.go

@@ -16,6 +16,7 @@ func hasColumn(rows *sql.Rows, colname string) (bool, error) {
 			dests[i] = new(interface{})
 		}
 	}
+	defer rows.Close()
 	for rows.Next() {
 		rows.Scan(dests...)
 		if name == colname {