add filter icon

ui/theme/theme.go

@@ -121,6 +121,7 @@ var (
 	PlaylistIcon    fyne.Resource
 	ShuffleIcon     fyne.Resource
 	TracksIcon      fyne.Resource
+	FilterIcon      fyne.Resource = theme.NewThemedResource(res.ResFilterSvg)
 )
 
 // MUST be called at startup!

ui/widgets/albumfilterbutton.go

@@ -27,7 +27,7 @@ func NewAlbumFilterButton(filter *backend.AlbumFilter) *AlbumFilterButton {
 	a := &AlbumFilterButton{
 		filter: filter,
 		Button: widget.Button{
-			Icon: theme.AlbumIcon,
+			Icon: theme.FilterIcon,
 		},
 	}
 	a.OnTapped = a.showFilterDialog