Fix NoViableAltException with boolean expression in OrderBy clause

Fixes #1000

Author: hazzik

src/NHibernate.Test/Async/Linq/ByMethod/OrderByTests.cs

@@ -242,5 +242,19 @@ public async Task OrderByWithSelectDistinctAndTakeAsync()
 		{
 			await (db.Orders.Select(o => o.ShippedTo).Distinct().OrderBy(o => o).Take(1000).ToListAsync());
 		}
+		
+		[Test]
+		public async Task BooleanOrderByDescendingClauseAsync()
+		{
+			var query = from c in db.Customers
+			            orderby c.Address.Country == "Belgium" descending, c.Address.Country
+			            select c;
+
+			var customers = await (query.ToListAsync());
+			if (customers.Count > 1)
+			{
+				Assert.That(customers[0].Address.Country, Is.EqualTo("Belgium"));
+			}
+		}
 	}
 }

src/NHibernate.Test/Linq/ByMethod/OrderByTests.cs

@@ -230,5 +230,19 @@ public void OrderByWithSelectDistinctAndTake()
 		{
 			db.Orders.Select(o => o.ShippedTo).Distinct().OrderBy(o => o).Take(1000).ToList();
 		}
+		
+		[Test]
+		public void BooleanOrderByDescendingClause()
+		{
+			var query = from c in db.Customers
+			            orderby c.Address.Country == "Belgium" descending, c.Address.Country
+			            select c;
+
+			var customers = query.ToList();
+			if (customers.Count > 1)
+			{
+				Assert.That(customers[0].Address.Country, Is.EqualTo("Belgium"));
+			}
+		}
 	}
 }

src/NHibernate/Linq/Visitors/QueryModelVisitor.cs

@@ -474,10 +474,12 @@ public override void VisitOrderByClause(OrderByClause orderByClause, QueryModel
 		{
 			foreach (var clause in orderByClause.Orderings)
 			{
-				_hqlTree.AddOrderByClause(HqlGeneratorExpressionVisitor.Visit(clause.Expression, VisitorParameters).AsExpression(),
-								clause.OrderingDirection == OrderingDirection.Asc
-									? _hqlTree.TreeBuilder.Ascending()
-									: (HqlDirectionStatement)_hqlTree.TreeBuilder.Descending());
+				var orderBy = HqlGeneratorExpressionVisitor.Visit(clause.Expression, VisitorParameters).ToArithmeticExpression();
+				var direction = clause.OrderingDirection == OrderingDirection.Asc
+					? _hqlTree.TreeBuilder.Ascending()
+					: (HqlDirectionStatement)_hqlTree.TreeBuilder.Descending();
+
+				_hqlTree.AddOrderByClause(orderBy, direction);
 			}
 		}