Fix randAccess setting in ReadRecord()

Commit 38a95731 got this backwards.

Author: Kyotaro Horiguchi
Discussion: https://www.postgresql.org/message-id/20200128.194408.2260703306774646445.horikyota.ntt@gmail.com

src/backend/access/transam/xlog.c

@@ -4265,7 +4265,7 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 	/* Pass through parameters to XLogPageRead */
 	private->fetching_ckpt = fetching_ckpt;
 	private->emode = emode;
-	private->randAccess = (xlogreader->ReadRecPtr != InvalidXLogRecPtr);
+	private->randAccess = (xlogreader->ReadRecPtr == InvalidXLogRecPtr);
 
 	/* This is the first attempt to read this page. */
 	lastSourceFailed = false;