better version of Join and undo unrelated change

Author: bahusoid

src/NHibernate/Hql/Ast/ANTLR/Tree/ResultVariableRefNode.cs

@@ -67,7 +67,7 @@ private SqlString GetColumnPositionsString(int scalarColumnIndex)
 
 		private SqlString GetColumnNamesString(int scalarColumnIndex)
 		{
-			return SqlStringHelper.Join(", ", Walker.SelectClause.ColumnNames[scalarColumnIndex]);
+			return SqlStringHelper.Join(new SqlString(", "), Walker.SelectClause.ColumnNames[scalarColumnIndex]);
 		}
 	}
 }

src/NHibernate/SqlCommand/SqlStringHelper.cs

@@ -31,20 +31,20 @@ public static SqlString Join(SqlString separator, IEnumerable objects)
 			return buf.ToSqlString();
 		}
 
-		public static SqlString Join(string separator, IEnumerable objects)
+		internal static SqlString Join(string separator, IList<SqlString> strings)
 		{
-			SqlStringBuilder buf = new SqlStringBuilder();
-			bool first = true;
+			if(strings.Count == 0)
+				return SqlString.Empty;
 
-			foreach (object obj in objects)
-			{
-				if (!first)
-				{
-					buf.Add(separator);
-				}
+			if (strings.Count == 1)
+				return strings[0];
 
-				first = false;
-				buf.AddObject(obj);
+			var buf = new SqlStringBuilder(strings.Count * 2 + 1);
+
+			buf.Add(strings[0]);
+			for (var index = 1; index < strings.Count; index++)
+			{
+				buf.Add(separator).Add(strings[index]);
 			}
 
 			return buf.ToSqlString();