#20288: fix handling of invalid numeric charrefs in HTMLParser.

Lib/test/test_htmlparser.py

@@ -151,6 +151,12 @@ text
             ("data", "&#bad;"),
             ("endtag", "p"),
         ])
+        # add the [] as a workaround to avoid buffering (see #20288)
+        self._run_check(["<div>&#bad;</div>"], [
+            ("starttag", "div", []),
+            ("data", "&#bad;"),
+            ("endtag", "div"),
+        ])
 
     def test_unclosed_entityref(self):
         self._run_check("&entityref foo", [