[3.12] gh-123133: clarify p=0 case for "f" and "e" formatting types (GH-125426) (#125429)

gh-123133: clarify p=0 case for "f" and "e" formatting types (GH-125426)
(cherry picked from commit cfc27bc50fe165330f2295f9ac0ad56ca5b0f31c)

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>