clean output buffer for Throwable instead of just Exception

Fixes #514

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Output buffer is now cleaned for internal PHP errors as well, not just for Exceptions [#514](https://github.com/smarty-php/smarty/issues/514)
+
 ## [4.2.1] - 2022-09-14
 
 ### Security

libs/sysplugins/smarty_internal_templatebase.php

@@ -257,7 +257,7 @@ abstract class Smarty_Internal_TemplateBase extends Smarty_Internal_Data
                 error_reporting($_smarty_old_error_level);
             }
             return $result;
-        } catch (Exception $e) {
+        } catch (Throwable $e) {
             while (ob_get_level() > $level) {
                 ob_end_clean();
             }