open media state added

app/loopedworld/src/main/java/su/rst10h/loopedworld/HelloSurface.kt

@@ -200,21 +200,25 @@ class HelloSurface : SurfaceView, SurfaceHolder.Callback {
         }
     }
     fun render() {
-        persistentSurface?.let {
-            val pCanvas = it.lockCanvas(null)
-            clearCanvas(pCanvas)
-            synchronized(it) {
-                drawHello(pCanvas, _frameNumber)
+        persistentSurface?.let {surface ->
+            val pCanvas = surface.lockCanvas(null)
+            pCanvas?.let {
+                clearCanvas(it)
+                synchronized(surface) {
+                    drawHello(it, _frameNumber)
+                }
+                surface.unlockCanvasAndPost(pCanvas)
             }
-            it.unlockCanvasAndPost(pCanvas)
         }
     }
 
     fun preview() {
         val canvas = holder.lockCanvas()
-        clearCanvas(canvas)
-        drawHello(canvas, _frameNumber)
-        holder.unlockCanvasAndPost(canvas)
+        canvas?.let {
+            clearCanvas(it)
+            drawHello(it, _frameNumber)
+            holder.unlockCanvasAndPost(it)
+        }
     }
 
     override fun surfaceChanged(holder: SurfaceHolder, format: Int, width: Int, height: Int) {