[REMI] [Correct] At least one bin is needed for hist2d

Description

If only one hit is found, as in p4796 r142, the notebook tries to call ax.hist2d with 0 bins in the TOF dimension, which fails:

Traceback

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-18-a09f53e9c2df> in <module>
     28     for ax, dim_label in zip([txp, typ], ['x', 'y']):
     29         ax.hist2d(flat_hits['t'], flat_hits[dim_label], bins=(int((max_tof - min_tof) // 5), 256),
---> 30                    range=[[min_tof, max_tof], [-im_radius, im_radius]], norm=LogNorm())
     31         ax.set_ylabel(f'{dim_label.upper()} / mm')
     32 

/gpfs/exfel/sw/software/exfel_environments/sqs-remi-preview/lib/python3.7/site-packages/matplotlib/__init__.py in inner(ax, data, *args, **kwargs)
   1350     def inner(ax, *args, data=None, **kwargs):
   1351         if data is None:
-> 1352             return func(ax, *map(sanitize_sequence, args), **kwargs)
   1353 
   1354         bound = new_sig.bind(ax, *args, **kwargs)

/gpfs/exfel/sw/software/exfel_environments/sqs-remi-preview/lib/python3.7/site-packages/matplotlib/axes/_axes.py in hist2d(self, x, y, bins, range, density, weights, cmin, cmax, **kwargs)
   7071 
   7072         h, xedges, yedges = np.histogram2d(x, y, bins=bins, range=range,
-> 7073                                            density=density, weights=weights)
   7074 
   7075         if cmin is not None:

<__array_function__ internals> in histogram2d(*args, **kwargs)

/gpfs/exfel/sw/software/exfel_environments/sqs-remi-preview/lib/python3.7/site-packages/numpy/lib/twodim_base.py in histogram2d(x, y, bins, range, normed, weights, density)
    742         xedges = yedges = asarray(bins)
    743         bins = [xedges, yedges]
--> 744     hist, edges = histogramdd([x, y], bins, range, normed, weights, density)
    745     return hist, edges[0], edges[1]
    746 

<__array_function__ internals> in histogramdd(*args, **kwargs)

/gpfs/exfel/sw/software/exfel_environments/sqs-remi-preview/lib/python3.7/site-packages/numpy/lib/histograms.py in histogramdd(sample, bins, range, normed, weights, density)
   1046             if bins[i] < 1:
   1047                 raise ValueError(
-> 1048                     '`bins[{}]` must be positive, when an integer'.format(i))
   1049             smin, smax = _get_outer_edges(sample[:,i], range[i])
   1050             try:

ValueError: `bins[0]` must be positive, when an integer

I have prepared this in case a hotfix is needed, but the main problem I was called for seems to be a migration issue: https://redmine.xfel.eu/issues/151221

How Has This Been Tested?

Modifying the failing notebook and running interactively

Relevant Documents (optional)

SQS_REMI_DLD6_correct_004796_r142_230407_062019.pdf

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.

Reviewers

@schmidtp