BUG: Logarithmic colorscaling issue with magspect()

[KCollins]

Steps to reproduce:

magspect(parameter = "By", start = datetime.datetime(2015, 3, 25, 17, 50), end = datetime.datetime(2015, 3, 25, 19, 50), is_logcolor = False)
magspect(parameter = "By", start = datetime.datetime(2015, 3, 25, 17, 50), end = datetime.datetime(2015, 3, 25, 19, 50), is_logcolor = True)

The first command yields a plot; the second one generates this error:

File [~/.local/lib/python3.9/site-packages/matplotlib/colors.py:1788](http://localhost:8888/~/.local/lib/python3.9/site-packages/matplotlib/colors.py#line=1787), in _make_norm_from_scale.<locals>.Norm.__call__(self, value, clip)
   1786 t_vmin, t_vmax = self._trf.transform([self.vmin, self.vmax])
   1787 if not np.isfinite([t_vmin, t_vmax]).all():
-> 1788     raise ValueError("Invalid vmin or vmax")
   1789 t_value -= t_vmin
   1790 t_value /= (t_vmax - t_vmin)

ValueError: Invalid vmin or vmax