check if media_list_player->media_list is null before locking - fixes #1524

bindings/java/core/src/test/java/org/videolan/jvlc/internal/MediaListPlayerTest.java

@@ -101,15 +101,13 @@ public class MediaListPlayerTest
         Assert.assertEquals(0, exception.raised);
     }
 
-//    @Test
-    /**
-     * This test is disabled: see https://trac.videolan.org/vlc/ticket/1524
-     */
+    @Test
     public void mediaListPlayerPlayNoItemTest()
     {
         libvlc_exception_t exception = new libvlc_exception_t();
         LibVlcMediaListPlayer mediaListPlayer = libvlc.libvlc_media_list_player_new(libvlcInstance, exception);
         libvlc.libvlc_media_list_player_play(mediaListPlayer, exception);
+        Assert.assertEquals(1, exception.raised);
     }
 
 }

src/control/media_list_player.c

@@ -40,6 +40,7 @@ get_next_path( libvlc_media_list_player_t * p_mlp )
     libvlc_media_list_path_t ret;
     libvlc_media_list_t * p_parent_of_playing_item;
     libvlc_media_list_t * p_sublist_of_playing_item;
+
     p_sublist_of_playing_item = libvlc_media_list_sublist_at_path(
                             p_mlp->p_mlist,
                             p_mlp->current_playing_item_path );
@@ -428,6 +429,12 @@ void libvlc_media_list_player_next( libvlc_media_list_player_t * p_mlp,
 {    
     libvlc_media_list_path_t path;
 
+    if (! p_mlp->p_mlist )
+    {
+        libvlc_exception_raise( p_e, "No more element to play" );
+        return;
+    }
+    
     libvlc_media_list_lock( p_mlp->p_mlist );
 
     path = get_next_path( p_mlp );