Fix an oversight in format 2: nextlsn

Format 2 (1b0cbac) forgot to add
nextlsn. Format 1 includes this information if include-lsn is provided.
This information can be useful for applications that use LSN position as
a restart point.

wal2json.c

@@ -853,6 +853,10 @@ pg_decode_begin_txn_v2(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
 		char *lsn_str = DatumGetCString(DirectFunctionCall1(pg_lsn_out, UInt64GetDatum(txn->final_lsn)));
 		appendStringInfo(ctx->out, ",\"lsn\":\"%s\"", lsn_str);
 		pfree(lsn_str);
+
+		lsn_str = DatumGetCString(DirectFunctionCall1(pg_lsn_out, UInt64GetDatum(txn->end_lsn)));
+		appendStringInfo(ctx->out, ",\"nextlsn\":\"%s\"", lsn_str);
+		pfree(lsn_str);
 	}
 
 	appendStringInfoChar(ctx->out, '}');
@@ -931,6 +935,10 @@ pg_decode_commit_txn_v2(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 		char *lsn_str = DatumGetCString(DirectFunctionCall1(pg_lsn_out, UInt64GetDatum(commit_lsn)));
 		appendStringInfo(ctx->out, ",\"lsn\":\"%s\"", lsn_str);
 		pfree(lsn_str);
+
+		lsn_str = DatumGetCString(DirectFunctionCall1(pg_lsn_out, UInt64GetDatum(txn->end_lsn)));
+		appendStringInfo(ctx->out, ",\"nextlsn\":\"%s\"", lsn_str);
+		pfree(lsn_str);
 	}
 
 	appendStringInfoChar(ctx->out, '}');