fix SqlCriteria count

Model/SqlCriteria.php

@@ -82,7 +82,12 @@ class SqlCriteria
     public function count()
     {
 	    $this->defineJoinExpressions();
+        $sql_expression_backup = $this->sql_expression;
+        if (!$this->sql_expression) {
+            $this->sql_expression = 'SELECT COUNT(*) as count FROM :table';
+        }
         $count = $this->model->count(array(), '', $this->where, null, $this->group_by, $this->sql_expression, $this->sql_expression_params)->fetchField('count');
+        $this->sql_expression = $sql_expression_backup;
 	    return $count;
     }