Bug: toml-sort moves and entries to different groups

[15r10nk]

This bug was reported here https://github.com/macisamuele/language-formatters-pre-commit-hooks/issues/198, but it is actually a bug in toml-sort.

The minimal reproducible toml file for this error is

[x]
v.w = ""

[x.r]

which gets formatted to:

[x]

[x.r]
v.w = ""