Fixed 'java.lang.IllegalArgumentException: Undeclared path ...' when creating order by with subquery

Hi,

After migrating from  3_2_3 to 3_5_1 we begin to see the following exception:
````
java.lang.IllegalArgumentException: Undeclared path 'cat'. Add this path as a source to the query to be able to reference it.
	at com.mysema.query.types.ValidatingVisitor.visit(ValidatingVisitor.java:78)
	at com.mysema.query.types.ValidatingVisitor.visit(ValidatingVisitor.java:1)
	at com.mysema.query.types.path.BeanPath.accept(BeanPath.java:75)
	at com.mysema.query.types.ValidatingVisitor.visit(ValidatingVisitor.java:65)
	at com.mysema.query.types.ValidatingVisitor.visit(ValidatingVisitor.java:1)
	at com.mysema.query.types.OperationImpl.accept(OperationImpl.java:90)
	at com.mysema.query.DefaultQueryMetadata.validate(DefaultQueryMetadata.java:351)
	at com.mysema.query.DefaultQueryMetadata.addJoin(DefaultQueryMetadata.java:155)
	at com.mysema.query.support.QueryMixin.leftJoin(QueryMixin.java:314)
	at com.mysema.query.jpa.JPAQueryMixin.shorten(JPAQueryMixin.java:122)
	at com.mysema.query.jpa.JPAQueryMixin.convertPathForOrder(JPAQueryMixin.java:149)
	at com.mysema.query.jpa.JPAQueryMixin.access$0(JPAQueryMixin.java:135)
	at com.mysema.query.jpa.JPAQueryMixin$1.visit(JPAQueryMixin.java:171)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:1)
	at com.mysema.query.types.PathImpl.accept(PathImpl.java:94)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:162)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:49)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:1)
	at com.mysema.query.types.OperationImpl.accept(OperationImpl.java:90)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:128)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:1)
	at com.mysema.query.types.SubQueryExpressionImpl.accept(SubQueryExpressionImpl.java:57)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:162)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:49)
	at com.mysema.query.support.ReplaceVisitor.visit(ReplaceVisitor.java:1)
	at com.mysema.query.types.OperationImpl.accept(OperationImpl.java:90)
	at com.mysema.query.jpa.JPAQueryMixin.convert(JPAQueryMixin.java:175)
	at com.mysema.query.support.QueryMixin.orderBy(QueryMixin.java:356)
	at com.mysema.query.support.QueryMixin.orderBy(QueryMixin.java:367)
	at com.mysema.query.support.QueryBase.orderBy(QueryBase.java:107)
	at com.mysema.query.jpa.JPAQueryBase.orderBy(JPAQueryBase.java:1)
	at com.mysema.query.jpa.SubQueryTest.OrderBy(SubQueryTest.java:199)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
````

I investigate a little bit, and notice the 3_2_3 behaves like convert was call passing false intead