Improve 'item not found' pages (#3438)

* Make scene 'not found' page consistent
* Make backend response for no result consistent

internal/api/resolver_query_find_performer.go

@@ -2,6 +2,8 @@ package api
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 	"strconv"
 
 	"github.com/stashapp/stash/pkg/models"
@@ -16,7 +18,7 @@ func (r *queryResolver) FindPerformer(ctx context.Context, id string) (ret *mode
 	if err := r.withReadTxn(ctx, func(ctx context.Context) error {
 		ret, err = r.repository.Performer.Find(ctx, idInt)
 		return err
-	}); err != nil {
+	}); err != nil && !errors.Is(err, sql.ErrNoRows) {
 		return nil, err
 	}