Fix crash reported by Steve

Steps to reproduce:
1) Launch Audacity
2) File > New
3) Generate a sound in the new project
4) Open a LADSPA effect
5) In second project: File > Close, don't save changes.
6) In first project, generate a sound.
7) Click "Play" button - crash :-(

src/effects/Effect.cpp

@@ -2192,6 +2192,19 @@ EffectUIHost::~EffectUIHost()
 {
    if (mInitialized)
    {
+      mInitialized = false;
+
+      wxTheApp->Disconnect(EVT_AUDIOIO_PLAYBACK,
+                           wxCommandEventHandler(EffectUIHost::OnPlayback),
+                           NULL,
+                           this);
+
+      wxTheApp->Disconnect(EVT_AUDIOIO_CAPTURE,
+                           wxCommandEventHandler(EffectUIHost::OnCapture),
+                           NULL,
+                           this);
+
+      EffectManager::Get().RealtimeRemoveEffect(mEffect);
    }
 
    if (mClient)