[PATCH] /src/backend/access/transam/xlog.c, tiny improvements

Hi,
There are 3 tiny improvements to xlog.c code:

1. At function StartupXLOG (line 6370), the second test if
(ArchiveRecoveryRequested) is redundant and can secure removed.
2. At function StartupXLOG (line 7254) the var switchedTLI already been
tested before and the second test can secure removed.
3. At function KeepLogSeg (line 9357) the test if (slotSegNo <= 0), the
var slotSegNo is uint64 and not can be < 0.

As it is a critical file, even though small, these improvements, I believe
are welcome, because they improve readability.

regards,
Ranier Vilela