XE 581: Folder tree loses custom color after Dual/one toggle

[JohnFredC]

To reproduce:

• 1. Set custom colors for the folder tree
  2. Display 2 panels
  3. Display the folder tree in each panel (i.e., show two trees)
  4. Issue Dual/one panel to switch to one panel mode
  5. Issue Dual/one panel to switch back to two panel mode
  6. Observe that the tree colors of the inactive panel have reverted to default

[Marek]

Fixed for the release 582.