Always remove delimiters to avoid quadratic behavior.

Author: kevinbackhouse

extensions/strikethrough.c

@@ -67,6 +67,7 @@ static delimiter *insert(cmark_syntax_extension *self, cmark_parser *parser,
   strikethrough->end_column = closer->inl_text->start_column + closer->inl_text->as.literal.len - 1;
   cmark_node_free(closer->inl_text);
 
+done:
   delim = closer;
   while (delim != NULL && delim != opener) {
     tmp_delim = delim->previous;
@@ -76,7 +77,6 @@ static delimiter *insert(cmark_syntax_extension *self, cmark_parser *parser,
 
   cmark_inline_parser_remove_delimiter(inline_parser, opener);
 
-done:
   return res;
 }