Fix more portability issues with casts to Size when using off_t

Michael Paquier <michael@paquier.xyz>

Commit: 94019c879a138454af723fa8bfc346d4a44ecd47
Author: Michael Paquier <michael@paquier.xyz>
Date: 2018-07-18T00:51:53Z
Releases: 12.0
Fix more portability issues with casts to Size when using off_t

This should tame the beast, as there are no other places where off_t is
used in the new error messages.

Reported again by longfin, which complained about walsender.c while I
spotted the other two ones while double-checking.

Files