Disable multithreaded scanners for sqlite

as it's not reliable

api/graphql/resolvers/scanner.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"time"
 
+	"github.com/photoview/photoview/api/database/drivers"
 	"github.com/photoview/photoview/api/graphql/models"
 	"github.com/photoview/photoview/api/scanner"
 	"github.com/pkg/errors"
@@ -66,6 +67,10 @@ func (r *mutationResolver) SetScannerConcurrentWorkers(ctx context.Context, work
 		return 0, errors.New("concurrent workers must at least be 1")
 	}
 
+	if workers > 1 && drivers.DatabaseDriver() == drivers.DatabaseDriverSqlite {
+		return 0, errors.New("multiple workers not supported for SQLite databases")
+	}
+
 	if err := r.Database.Session(&gorm.Session{AllowGlobalUpdate: true}).Model(&models.SiteInfo{}).Update("concurrent_workers", workers).Error; err != nil {
 		return 0, err
 	}