Fix crash in csv reader.

Veusz version: 1.21
Python version: 2.7.6 (default, Nov 10 2013, 19:24:18) [MSC v.1500 32 bit (Intel)]
Python platform: win32
Numpy version: 1.8.0
Qt version: 4.8.5
PyQt version: 4.10.3
SIP version: 4.15.3
Date: Fri, 15 Aug 2014 16:45:41 +0000

Traceback (most recent call last):
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dialogs.importdialog", line 277, in slotImport
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.dialog_csv", line 193, in doImport
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.document.doc", line 191, in applyOperation
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.base", line 249, in do
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.defn_csv", line 71, in doImport
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.readcsv", line 348, in readData
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.readcsv", line 268, in _handleVal
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.readcsv", line 210, in _newValueInBlankColumn
  File "C:\src\veusz-msvc\veusz\build\veusz_windows_pyinst\out00-PYZ.pyz\veusz.dataimport.readcsv", line 139, in _getNameAndColType
KeyError: 1