fpvviewer: Fixes token debug for sequential pages

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@3592 8e941d3f-bd1b-0410-a28a-d453659cc2b4

applications/fpvviewer/fpvv_mainform.pas

@@ -332,7 +332,10 @@ begin
 
     // Generate the positioning info
     for i := 0 to Vec.GetPageCount()-1 do
+    begin
+      if Vec.GetPageAsVectorial(i) <> nil then
         Vec.GetPageAsVectorial(i).PositionEntitySubparts(Canvas, 0, 0);
+    end;
 
     TokensTreeView.Items.Clear;
     Vec.GenerateDebugTree(@FPVDebugAddItemProc);