Fix for Novell bug 519648

When passing "new object [] {null}" as argument to DataRowCollection.Find() we get a IndexOutOfRangeException on Mono whereas on Windows it just returns (https://bugzilla.novell.com/show_bug.cgi?id=519648). This change adds two unit tests that demonstrate the problem and modifies the behaviour to match that on .NET when passing a null object or an array with a null object.