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.

src/backend/replication/walsender.c

@@ -509,7 +509,7 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 		else if (nread == 0)
 			ereport(ERROR,
 					(errmsg("could not read file \"%s\": read %d of %zu",
-							path, nread, bytesleft)));
+							path, nread, (Size) bytesleft)));
 
 		pq_sendbytes(&buf, rbuf, nread);
 		bytesleft -= nread;