src: do not make `Resize(0)`’d buffers base `nullptr`

This fixes issues in which APIs that accept pointers created this way
treat `nullptr` and a zero-length buffer differently.
We already do something similar for our `Malloc()` implementation.

PR-URL: https://github.com/nodejs/node/pull/26731
Fixes: https://github.com/nodejs/node/issues/26514


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>