[ticket/16955] Clean up code in db classes

PHPBB3-16955

phpBB/phpbb/db/tools/doctrine.php

@@ -462,7 +462,8 @@ class doctrine implements tools_interface
 		}
 		catch (Exception $e)
 		{
-			return $e->getMessage();
+			// @todo: check if it makes sense to properly handle the exception
+			return false;
 		}
 	}