console: minor timeLogImpl() refactor

This commit does two things:

- Reverses the boolean value returned by timeLogImpl(). The new
  values make more sense semantically (IMO anyway), and save a
  a single NOT operation.
- Explicitly check for undefined when calling _times.get()
  instead of coercing the value.

PR-URL: https://github.com/nodejs/node/pull/29100


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>