Fixed issue #1314: Make fixed columns non-draggable

Author: joachimmarder

Source/VirtualTrees.Header.pas

@@ -3243,6 +3243,8 @@ procedure TVirtualTreeColumn.SetOptions(Value : TVTColumnOptions);
     ToBeSet := Value - FOptions;
 
     FOptions := Value;
+    if coFixed in ToBeSet then
+      FOptions := FOptions - [coDraggable]; // issue #1314
 
     VisibleChanged := coVisible in (ToBeSet + ToBeCleared);
     lParentColorSet := coParentColor in ToBeSet;