macosx: work-around a racing condition (close #6412)

(cherry picked from commit 6cbf48f1f9c38c1a0ed91fb6699f977b3b7f97ea)

modules/gui/macosx/playlistinfo.h

@@ -98,6 +98,8 @@
     VLCInfoTreeItem * rootItem;
 
     input_item_t * p_item;
+
+    BOOL b_awakeFromNib;
 }
 
 - (void)initPanel;

modules/gui/macosx/playlistinfo.m

@@ -121,6 +121,8 @@ static VLCInfo *_o_sharedInstance = nil;
     [o_info_window setInitialFirstResponder: o_uri_txt];
     [o_info_window setDelegate: self];
 
+    b_awakeFromNib = YES;
+
     /* We may be awoken from nib way after initialisation
      * Update ourselves */
     [self updatePanelWithItem:p_item];
@@ -278,6 +280,9 @@ static VLCInfo *_o_sharedInstance = nil;
 
 - (void)updateStatistics
 {
+    if (!b_awakeFromNib)
+        return;
+
     if ([o_info_window isVisible])
     {
         if( !p_item || !p_item->p_stats )