Adding a 0.00 charge object results in crash

[ghost]

The contour plot crashes for some reason [1] with stacktrace [2] when a 0.00 charge is added as the only object.

A more fundamental question is whether to allow 0.00 charges and if that makes physics sense - then stop the user with a warning before even calling the python exec.

[1] https://github.com/palkiakerr/ProjectX_Workspace/blob/4ef9ed7e0f7dcdb1afa447e49966305854b87954/src/Plotter.py#L72

[2]

/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/contour.py:1230: UserWarning: No contour levels were found within the data range.
  warnings.warn("No contour levels were found"
Traceback (most recent call last):
  File "Plotter.py", line 82, in <module>
    main()
  File "Plotter.py", line 72, in main
    plt.colorbar()
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/pyplot.py", line 2320, in colorbar
    ret = gcf().colorbar(mappable, cax = cax, ax=ax, **kw)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/figure.py", line 2098, in colorbar
    cb = cbar.colorbar_factory(cax, mappable, **cb_kw)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 1399, in colorbar_factory
    cb = Colorbar(cax, mappable, **kwargs)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 935, in __init__
    ColorbarBase.__init__(self, ax, **kw)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 327, in __init__
    self.draw_all()
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 353, in draw_all
    self._config_axes(X, Y)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 437, in _config_axes
    xy = self._outline(X, Y)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/matplotlib/colorbar.py", line 485, in _outline
    x = np.take(np.ravel(np.transpose(X)), ii)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/numpy/core/fromnumeric.py", line 189, in take
    return _wrapfunc(a, 'take', indices, axis=axis, out=out, mode=mode)
  File "/workspace/ProjectX_Workspace/venv/local/lib/python2.7/site-packages/numpy/core/fromnumeric.py", line 56, in _wrapfunc
    return getattr(obj, method)(*args, **kwds)
IndexError: index 2 is out of bounds for size 2