fix count method with saving original sql expression

Model/SqlCriteria.php

@@ -81,9 +81,11 @@ class SqlCriteria
 
     public function count($select = 'x')
     {
-	    $sql_expression_backup = $this->sql_expression;
-	    $this->select($select);
 	    $this->defineJoinExpressions();
+	    $sql_expression_backup = $this->sql_expression;
+	    if ($select) {
+		    $this->select( $select );
+	    }
         if (!$this->sql_expression) {
             $this->sql_expression = 'SELECT COUNT(*) as count FROM :table';
         }