IndexColumn name is defined on creation

Fixes issue when some columns aren't indexed by name

Author: alex-kulakov

Orm/Xtensive.Orm/Sql/Model/IndexColumn.cs

@@ -90,7 +90,7 @@ public bool Ascending
     /// <value></value>
     public override string Name
     {
-      get { return !expression.IsNullReference() ? string.Empty : column.Name; }
+      get { return base.Name; }
       set { throw new NotSupportedException(); }
     }
 
@@ -142,13 +142,15 @@ void IPairedNode<Index>.UpdatePairedProperty(string property, Index value)
     #region Constructors
 
     internal IndexColumn(Index index, DataTableColumn column, bool ascending)
+      : base(column.Name)
     {
       Column = column;
       Index = index;
       this.ascending = ascending;
     }
 
     internal IndexColumn(Index index, SqlExpression expression, bool ascending)
+      : base(string.Empty)
     {
       this.expression = expression;
       Index = index;