Problems with Basemap.scatter

Hi,

I have stumbled over a bug in scatter plot. With latlon=True, it crashes with zero, one or two points.

Example code:

import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap

bmap = Basemap(projection='merc',
               llcrnrlon=9, urcrnrlon=13,
               llcrnrlat=63, urcrnrlat=65,
               resolution='c')

lon = [10.0, 12.0]
lat = [64.0, 65.0]

bmap.scatter(lon, lat, latlon=True)

plt.show()

This crashes with the following Traceback:

Traceback (most recent call last):
  File "a.py", line 12, in <module>
    bmap.scatter(lon, lat, latlon=True)
  File "/opt/anaconda/lib/python2.7/site-packages/mpl_toolkits/basemap/__init__.py", line 536, in with_transform
    x = self.shiftdata(x)
  File "/opt/anaconda/lib/python2.7/site-packages/mpl_toolkits/basemap/__init__.py", line 4775, in shiftdata
    thresh = 360.-londiff_sort[-2]
IndexError: index -2 is out of bounds for axis 0 with size 1

I am using python 2.7.10, matplotlib 1.4.3, basemap 1.0.7 on a 64-bit Linux machine

Start by running the supplied Basemap.scatter example with latlon=True and inspect the shiftdata entry point in mpl_toolkits/basemap/init.py, where the traceback fails for small inputs. Done means scatter handles zero, one, and two points without raising IndexError.