fix: tx pointer reset with empty tx table

If the tx pointer becomes outdated, we want to reset it to the end of
the tx queue, so that we start decrypting at the next submitted tx. To
do that, we query the index of the latest tx and add 1. If the table is
empty, the SQL query will return NULL. However, SQLC will not pick up on
that and try to scan into an int32 value, resulting in an error.

This commit circumvents this by explicitly returning 0 instead of NULL in
the cases of an empty table and casting into a bigint, communicating the
expected type to SQLC.

Author: jannikluhn

rolling-shutter/keyperimpl/gnosis/database/gnosiskeyper.sqlc.gen.go

@@ -35,7 +35,9 @@ SET block_hash = $1, block_number = $2, slot = $3;
 SELECT * FROM transaction_submitted_events_synced_until LIMIT 1;
 
 -- name: GetTransactionSubmittedEventCount :one
-SELECT max(index) + 1 FROM transaction_submitted_event
+SELECT
+    cast(coalesce(max(index) + 1, 0) AS bigint)
+FROM transaction_submitted_event
 WHERE eon = $1;
 
 -- name: DeleteTransactionSubmittedEventsFromBlockNumber :exec

rolling-shutter/keyperimpl/gnosis/database/sql/queries/gnosiskeyper.sql

@@ -209,11 +209,8 @@ func getTxPointer(ctx context.Context, db *pgxpool.Pool, eon int64, maxTxPointer
 			Int64("tx-pointer", txPointer).
 			Int64("tx-pointer-age", txPointerAge).
 			Msg("outdated tx pointer")
-		txPointerInt32, err := gnosisKeyperDB.GetTransactionSubmittedEventCount(ctx, eon)
-		txPointer = int64(txPointerInt32)
-		if err == pgx.ErrNoRows {
-			txPointer = 0
-		} else if err != nil {
+		txPointer, err = gnosisKeyperDB.GetTransactionSubmittedEventCount(ctx, eon)
+		if err != nil {
 			return 0, errors.Wrap(err, "failed to query transaction submitted event count from db")
 		}
 	}