Initialize root window

This fixes the crash caused by:
>> demo

click on "R3GUI widgets"
click on "Select an option" and leave the dropdown menu open
move the window

It will crash with:
X Error of failed request:  BadWindow (invalid Window parameter)
Major opcode of failed request:  40 (X_TranslateCoords)
  Resource id in failed request:  0x0
  Serial number of failed request:  259
  Current serial number in output stream:  259