bug in popup button

[Benhur Stein]

Hi!
Some recent change in popup button code (I think) is causing the exception 
shown below.

It is caused after calling removeAllItems of a NSPopUpButton, but can probably 
be caused in other circumstances.
The NSControl below is a NSPopUpButton.

Looking at this backtrace it seems that the relationship among all the objects 
that make up
the popup button is intricate, and I did not feel like digging into it.

Benhur

#2  0x403ff5e0 in _c_NSException__raise_format_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-base.so.1
#3  0x403816b7 in _i_GSArray__objectAtIndex_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-base.so.1
#4  0x40152325 in _i_NSMenuView__menuItemCellForItemAtIndex_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-gui.so.0
#5  0x40170f83 in _i_NSPopUpButtonCell__drawWithFrame_inView_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-gui.so.0
#6  0x4010cbb6 in _i_NSControl__drawCell_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-gui.so.0
#7  0x4010cb32 in _i_NSControl__drawRect_ ()
  from 
/usr/local/GNUstep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu/libgnustep-gui.so.0