Standardize type of variable when extending Buffers

Hi,

This has already been discussed in [1].
But I thought it best to start a new thread.

The commit 31966b1
<https://github.com/postgres/postgres/commit/31966b151e6ab7a6284deab6e8fe5faddaf2ae4c>
introduced the infrastructure to extend
buffers.
But the patch mixed types with int and uint32.
The correct type of the variable counter is uint32.

Fix by standardizing the int type to uint32.

patch attached.

best regards,
Ranier Vilela

[1]
https://www.postgresql.org/message-id/CAEudQAr_oWHpZk4uumZijYS362gp4KHAah-yUe08CQY4a4SsOQ%40mail.gmail.com