Bugfix subplots legend plot spectra

[AEljarrat]

Dear all,

I like to use "hs.plot.plot_spectra" to do quick comparisons, especially since the animated legend allows me to set the visibility of the lines. It is also possible to use this command to fill several subplots in the same figure. However, in this case the animated legend cannot by used.

Description of the change

• This small PR fixes this bug.

Progress of the PR

• Change implemented.
• ready for review.

Minimal example of the bug fix or the new feature

>>> %matplotlib qt
>>> import matplotlib.pyplot as plt
>>> import hyperspy.api as hs
>>> import numpy as np
>>> 
>>> Ns = 5
>>> Nc = 256
>>> 
>>> data = np.random.rand(Ns, Nc)
>>> name = np.arange(Ns).astype('str')
>>> s    = hs.signals.Signal1D(data)
>>> 
>>> # This works
>>> hs.plot.plot_spectra(s.inav[:2], legend=name[:2])
>>> hs.plot.plot_spectra(s.inav[2:], legend=name[2:])
>>> 
>>> # This does not work
>>> f, ax = plt.subplots(1, 2)
>>> hs.plot.plot_spectra(s.inav[:2], legend=name[:2], fig=f, ax=ax[0])
>>> hs.plot.plot_spectra(s.inav[2:], legend=name[2:], fig=f, ax=ax[1])

Note that this example can be useful to update the user guide.

[ericpre]

Nice thanks!