Issue #7820: The parser tokenizer restores all bytes in the right if the BOM
check fails.

Fix an assertion in pydebug mode.
diff --git a/Misc/NEWS b/Misc/NEWS
index a02681a..086fb27 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #7820: The parser tokenizer restores all bytes in the right if
+  the BOM check fails.
+
 - Issue #7309: Fix unchecked attribute access when converting
   UnicodeEncodeError, UnicodeDecodeError, and UnicodeTranslateError to
   strings.