Fix missing return

Author: facelessuser

markdown/extensions/md_in_html.py

@@ -287,6 +287,7 @@ def parse_html_declaration(self, i: int) -> int:
                 if result == -1:
                     self.handle_data(self.rawdata[i:i + 1])
                     return i + 1
+                return result
             # The same override exists in `HTMLExtractor` without the check
             # for `mdstack`. Therefore, use parent of `HTMLExtractor` instead.
             return super(HTMLExtractor, self).parse_html_declaration(i)