[FIX] base: ir.http: only server_attachement for 404 errors

fixes #6792

openerp/addons/base/ir/ir_http.py

@@ -137,6 +137,7 @@ class ir_http(osv.AbstractModel):
     def _handle_exception(self, exception):
         # This is done first as the attachment path may
         # not match any HTTP controller.
+        if isinstance(exception, werkzeug.exceptions.HTTPException) and exception.code == 404:
             attach = self._serve_attachment()
             if attach:
                 return attach