segfault in QGridLayout.takeAt ( -1 )

This was originally filed as PySide bug 23.

Here is a simple test program to reproduce the crash:

import sys
from PySide.QtGui import *

app = QApplication ( sys.argv )
window = QFrame()
layout = QGridLayout ( window )
widget = layout.takeAt ( -1 )
window.show()
sys.exit ( app.exec_() )

Admittedly, -1 is not a valid index, but other layout classes handle the error
more gracefully. If QGridLayout is replaced by QVBoxLayout, for example,
takeAt(-1) returns None.

Although it may seem contrived to pass -1 to takeAt(), -1 is returned by
QGridLayout.indexOf() when passed an invalid widget.