Exception in SetDefaultNodeHeight when Parent = nil due to unconditional HandleNeeded() call #1366

Calling TBaseVirtualTree.SetDefaultNodeHeight can raise an exception when the control has no parent assigned (Parent = nil).

This happens because HandleNeeded() is invoked unconditionally when toAutoChangeScale is enabled. However, HandleNeeded() internally requires a valid parent window handle, which is not available when the control is not yet inserted into a parent.

Current Implementation:

if toAutoChangeScale in TreeOptions.AutoOptions then
  HandleNeeded();

Proposed Fix:

Add a guard to ensure Parent <> nil before calling HandleNeeded():

if (Parent <> nil) and (toAutoChangeScale in TreeOptions.AutoOptions) then
  HandleNeeded();