Clean up main playlist thread.

No useless wake up and simplify.
Fix a few race conditions with deactivation.

src/playlist/control.c

@@ -190,7 +190,10 @@ int playlist_PreparseEnqueue( playlist_t *p_playlist,
 {
     playlist_private_t *p_sys = pl_priv(p_playlist);
 
-    playlist_preparser_Push( p_sys->p_preparser, p_item );
+    PL_LOCK;
+    if( p_sys->p_preparser )
+        playlist_preparser_Push( p_sys->p_preparser, p_item );
+    PL_UNLOCK;
 
     return VLC_SUCCESS;
 }
@@ -200,7 +203,10 @@ int playlist_AskForArtEnqueue( playlist_t *p_playlist,
 {
     playlist_private_t *p_sys = pl_priv(p_playlist);
 
-    playlist_fetcher_Push( p_sys->p_fetcher, p_item );
+    PL_LOCK;
+    if( p_sys->p_fetcher )
+        playlist_fetcher_Push( p_sys->p_fetcher, p_item );
+    PL_UNLOCK;
 
     return VLC_SUCCESS;
 }

src/playlist/engine.c

@@ -174,11 +174,12 @@ static void playlist_Destructor( vlc_object_t * p_this )
     playlist_t *p_playlist = (playlist_t *)p_this;
     playlist_private_t *p_sys = pl_priv(p_playlist);
 
+    assert( !p_sys->p_input );
     assert( !p_sys->p_sout );
     assert( !p_sys->p_preparser );
     assert( !p_sys->p_fetcher );
 
-    msg_Err( p_this, "Destroyed" );
+    msg_Dbg( p_this, "Destroyed" );
 }
 
 /** Get current playing input.