Fix memory leak when doc comments are present before and after the parameter

Author: Christian Schneider

Zend/zend_language_parser.y

@@ -818,7 +818,7 @@ optional_cpp_modifiers:
 parameter:
 		optional_cpp_modifiers optional_type_without_static
 		is_reference is_variadic T_VARIABLE backup_doc_comment optional_property_hook_list backup_doc_comment
-			{ $$ = zend_ast_create_ex(ZEND_AST_PARAM, $1 | $3 | $4, $2, $5, NULL,
+			{ if ($6 && $8) { zend_string_release_ex($6, 0); }; $$ = zend_ast_create_ex(ZEND_AST_PARAM, $1 | $3 | $4, $2, $5, NULL,
 					NULL, $8 ? zend_ast_create_zval_from_str($8) : ($6 ? zend_ast_create_zval_from_str($6) : NULL), $7); }
 	|	optional_cpp_modifiers optional_type_without_static
 		is_reference is_variadic T_VARIABLE backup_doc_comment '=' expr optional_property_hook_list backup_doc_comment