Try to fix the following crash

Traceback (most recent call last):
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dialogs.dataeditdialog", line 91, in data
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.document.datasets", line 860, in uiDataItemToData
UnicodeDecodeError: 'ascii' codec can't decode byte 0xac in position 0: ordinal not in range(128)