Simplify xlogreader.c with XLogRec* macros

[邱宇航]

Hello hackers,

Commit 3f1ce97 refactored XLog record access macros, but missed in a few 
places. I fixed this, and patch is attached.

--
Yuhang Qiu

0001-Simplify-xlogreader.c-with-XLogRec-macros.patch
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