[lex.icon] "the sequence of (grammar term) octal-digits" does not cover the integer literal `0`

[morinmorin]

(Originally filed as cplusplus/draft#8380; resubmitting here as a CWG issue, because this is not editorial. With thanks to @eisenwave for the guidance.)

Full name of submitter: Masaki Moriguchi

Reference (section label): [lex.icon]

Issue description:
PR cplusplus/draft#3650 slimmed down [lex.icon] p1 to

In an integer-literal, the sequence of binary-digits, octal-digits, digits, or hexadecimal-digits is interpreted as a base N integer

However, this simplification appears to go a bit too far: in the (octal) integer literal 0, there are no octal-digits following the leading zero; so 0 falls outside this wording.

Decimal-literals have a similar issue: the leading nonzero-digit is not included in "the sequence of digits".

Suggested resolution:
Change in 5.3.2 [lex.icon] paragraph 1 as follows:

In an integer-literal,
the sequence of
- binary-digits,
- octal-digits,
- digits, or
- hexadecimal-digits
+  - binary-digits,
+  - 0 and zero or more octal-digits,
+  - nonzero-digit and zero or more digits, or
+  - hexadecimal-digits
is interpreted as a base N integer

Drafting note: The list is itemized for readability.