fs: fix `createReadStream(…, {end: n})` for non-seekable fds

82bdf8fb fixed an issue by silently modifying the `start`
option for the case when only `end` is passed, in order to perform
reads from a specified range in the file.

However, that approach does not work for non-seekable files, since
a numeric `start` option means that positioned reads will be used
to read data from the file.

This patch fixes that, and instead ends reading after a specified
size by adjusting the read buffer size.

This way we avoid re-introducing the bug that 82bdf8fb fixed,
and align behaviour with the native file stream mechanism
introduced in https://github.com/nodejs/node/pull/18936 as well.

PR-URL: https://github.com/nodejs/node/pull/19329
Fixes: https://github.com/nodejs/node/issues/19240
Refs: https://github.com/nodejs/node/pull/18121


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Chen Gang <gangc.cxy@foxmail.com>