[TrackerIcon] Fixed old-large icon removal

After downloading and resizing the new icon, we try to remove the downloaded
file, which is larger, but it fails because it tries to do so when the file
is still open, and therefor locked.
On close of the UI, we got `PermissionError` exceptions for each new icon.

deluge/ui/tracker_icons.py

@@ -479,14 +479,17 @@ class TrackerIcons(Component):
         # Requires Pillow(PIL) to resize.
         if icon and Image:
             filename = icon.get_filename()
+            remove_old = False
             with Image.open(filename) as img:
                 if img.size > (16, 16):
                     new_filename = filename.rpartition('.')[0] + '.png'
                     img = img.resize((16, 16), Image.ANTIALIAS)
                     img.save(new_filename)
                     if new_filename != filename:
-                        os.remove(filename)
-                        icon = TrackerIcon(new_filename)
+                        remove_old = True
+            if remove_old:
+                os.remove(filename)
+                icon = TrackerIcon(new_filename)
         return icon
 
     def store_icon(self, icon, host):