fix accidental concatenation

found by CodePro

h2/src/test/org/h2/test/jdbcx/TestConnectionPool.java

@@ -195,7 +195,7 @@ public class TestConnectionPool extends TestBase {
                         if (man.getActiveConnections() >= len + 1) {
                             throw new Exception("a: " +
                                     man.getActiveConnections()  +
-                                    " is not smaller than b: " + len + 1);
+                                    " is not smaller than b: " + (len + 1));
                         }
                         Statement stat = conn.createStatement();
                         stat.execute("SELECT 1 FROM DUAL");