Fix IndexError: invalid index to scalar variable

Fixes one test error on Python 2.x for Windows:
```
netcdf4-python version: 1.1.2
HDF5 lib version:       1.8.14
netcdf lib version:     4.3.2
numpy version           1.8.2
...............................E..................................
======================================================================
ERROR: runTest (tst_netcdftime.netcdftimeTestCase)
testing netcdftime
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\Build\netCDF4\netcdf4-python-static-git\test\tst_netcdftime.py", line 51, in runTest
    d2 = self.cdftime_mixed.num2date(t1)
  File "X:\Python27\lib\site-packages\netcdftime\netcdftime.py", line 824, in num2date
    date = DateFromJulianDay(jd, self.calendar)
  File "X:\Python27\lib\site-packages\netcdftime\netcdftime.py", line 290, in DateFromJulianDay
    month[month > 12] = month[month > 12] - 12
IndexError: invalid index to scalar variable.

----------------------------------------------------------------------
Ran 66 tests in 6.188s

FAILED (errors=1)
```