Report any XLogReadRecord() error in XlogReadTwoPhaseData().

Buildfarm members kittiwake and tadarida have witnessed errors at this
site.  The site discarded key facts.  Back-patch to v10 (all supported
versions).

Reviewed by Michael Paquier and Tom Lane.

Discussion: https://postgr.es/m/20211107013157.GB790288@rfd.leadboat.com

Author: nmisch

src/backend/access/transam/twophase.c

@@ -1397,10 +1397,18 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
 	record = XLogReadRecord(xlogreader, &errormsg);
 
 	if (record == NULL)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read two-phase state from WAL at %X/%X",
-						LSN_FORMAT_ARGS(lsn))));
+	{
+		if (errormsg)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read two-phase state from WAL at %X/%X: %s",
+							LSN_FORMAT_ARGS(lsn), errormsg)));
+		else
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read two-phase state from WAL at %X/%X",
+							LSN_FORMAT_ARGS(lsn))));
+	}
 
 	if (XLogRecGetRmid(xlogreader) != RM_XACT_ID ||
 		(XLogRecGetInfo(xlogreader) & XLOG_XACT_OPMASK) != XLOG_XACT_PREPARE)