shareable: Bug fix: Double free

internal/shareable/shareable.go

@@ -156,6 +156,9 @@ func (i *Image) forceShared() {
 	newI.replacePixels(pixels)
 	i.dispose(false)
 	*i = *newI
+	// TODO: This is a very tricky hack not to call Dispose twice for the same backend.
+	// Avoid such hack.
+	runtime.SetFinalizer(newI, nil)
 }
 
 func (i *Image) region() (x, y, width, height int) {

internal/shareable/shareable_test.go

@@ -18,6 +18,7 @@ import (
 	"errors"
 	"image/color"
 	"os"
+	"runtime"
 	"testing"
 
 	"github.com/hajimehoshi/ebiten"
@@ -183,4 +184,6 @@ func TestReshared(t *testing.T) {
 			}
 		}
 	}
+
+	runtime.GC()
 }