Fix "missing continuation record" after standby promotion

Invalidate abortedRecPtr and missingContrecPtr after a missing
continuation record is successfully skipped on a standby. This fixes a
PANIC caused when a recently promoted standby attempts to write an
OVERWRITE_RECORD with an LSN of the previously read aborted record.

Backpatch to 10 (all stable versions).

Author: Sami Imseih <simseih@amazon.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/44D259DE-7542-49C4-8A52-2AB01534DCA9@amazon.com

src/backend/access/transam/xlogrecovery.c

@@ -1948,6 +1948,10 @@ xlogrecovery_redo(XLogReaderState *record, TimeLineID replayTLI)
 				 LSN_FORMAT_ARGS(xlrec.overwritten_lsn),
 				 LSN_FORMAT_ARGS(record->overwrittenRecPtr));
 
+		/* We have safely skipped the aborted record */
+		abortedRecPtr = InvalidXLogRecPtr;
+		missingContrecPtr = InvalidXLogRecPtr;
+
 		ereport(LOG,
 				(errmsg("successfully skipped missing contrecord at %X/%X, overwritten at %s",
 						LSN_FORMAT_ARGS(xlrec.overwritten_lsn),

src/test/recovery/t/026_overwrite_contrecord.pl

@@ -13,7 +13,7 @@ use Test::More;
 # Test: Create a physical replica that's missing the last WAL file,
 # then restart the primary to create a divergent WAL file and observe
 # that the replica replays the "overwrite contrecord" from that new
-# file.
+# file and the standby promotes successfully.
 
 my $node = PostgreSQL::Test::Cluster->new('primary');
 $node->init(allows_streaming => 1);
@@ -100,6 +100,9 @@ like(
 	qr[successfully skipped missing contrecord at],
 	"found log line in standby");
 
+# Verify promotion is successful
+$node_standby->promote;
+
 $node->stop;
 $node_standby->stop;