Mandelbrot: Clean up thread handling code.

* Style fixes
 * Delete semaphores in destructor

Change-Id: Ia293d3f4096e2ef1305398356f3e263a8a263d78
Reviewed-on: https://review.haiku-os.org/c/866
Reviewed-by: waddlesplash <[email protected]>

src/apps/mandelbrot/FractalEngine.cpp

@@ -60,6 +60,8 @@ FractalEngine::FractalEngine(BHandler* parent, BLooper* looper)
 
 FractalEngine::~FractalEngine()
 {
+	delete_sem(fRenderSem);
+	delete_sem(fRenderStoppedSem);
 }
 
 
@@ -158,6 +160,7 @@ void FractalEngine::WriteToBitmap(BBitmap* bitmap)
 		B_RGB24);
 }
 
+
 void FractalEngine::StopRender()
 {
 	if (fRenderStopped)