buffer: zero-fill buffer allocated with invalid content

Zero-fill when `Buffer.alloc()` receives invalid fill data.

A solution like https://github.com/nodejs/node/pull/17427 which switches
to throwing makes sense, but is likely a breaking change.

This suggestion leaves the behaviour of `buffer.fill()` untouched,
since any change to it would be a breaking change, and lets
`Buffer.alloc()` check whether any filling took place or not.

PR-URL: https://github.com/nodejs/node/pull/17428
Refs: https://github.com/nodejs/node/pull/17427
Refs: https://github.com/nodejs/node/issues/17423


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>