Fix .plot() method for 1D data groups with no nxcoordinates

[stevenjgomez]

The recent addition of nxcoordinate logic to the plot.py module has broken some downstream behavior, in my case for the .plot() method of 1D data groups. The following is a minimal example to recreate the issue:

from nexusformat.nexus import *
import numpy as np

# Make 1D Gaussian
x = np.linspace(-10,10,51)
gaussian = np.exp(-x**2 / (2 * 1.0**2))

# Make NXaxes
X = NXfield(x, name='Qh')

# Make 1D NXdata
data_1D = NXdata(signal=gaussian, axes=X)

# Try to plot
data_1D.plot()

This raises the following:

Traceback (most recent call last):
  File "/Users/stevengomezalvarado/nxs_analysis_tools/scratch/reproduce_issue.py", line 15, in <module>
    data_1D.plot()
    ~~~~~~~~~~~~^^
  File "/Users/stevengomezalvarado/miniconda3/envs/nxs/lib/python3.13/site-packages/nexusformat/nexus/tree.py", line 7627, in plot
    plotview.plot(self, fmt, xmin=xmin, xmax=xmax, ymin=ymin, ymax=ymax,
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                  vmin=vmin, vmax=vmax, **kwargs)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/stevengomezalvarado/miniconda3/envs/nxs/lib/python3.13/site-packages/nexusformat/nexus/plot.py", line 273, in plot
    y = boundaries(axes[-2], data.shape[-2])
                   ~~~~^^^^
IndexError: list index out of range

The plot.py module contains the following if/else logic:

class PyplotPlotter:

    def plot(self, data_group, fmt=None, xmin=None, xmax=None,
             ymin=None, ymax=None, vmin=None, vmax=None, **kwargs):
        
        # Some code...

        try:
            
            # One-dimensional Plot
            if len(data.shape) == 1 and len(coordinates) == 0:
                # Some code
            
            if len(data.shape) == 1 and len(coordinates) > 0:
                # Some code
            
            # Two-dimensional plot
            else:
                # Some code

My assumption is that this if/if/else chain is actually meant to be an if/elif/else chain, which appears to resolve the issue and results in the expected behavior.

class PyplotPlotter:

    def plot(self, data_group, fmt=None, xmin=None, xmax=None,
             ymin=None, ymax=None, vmin=None, vmax=None, **kwargs):
        
        # Some code...

        try:
            
            # One-dimensional Plot
            if len(data.shape) == 1 and len(coordinates) == 0:
                # Some code
            
            elif len(data.shape) == 1 and len(coordinates) > 0:
                # Some code
            
            # Two-dimensional plot
            else:
                # Some code

Let me know your thoughts.

[rayosborn]

Thank you for the PR, which looks sound. It's a while since I made this change so I'm not sure why this problem has not appeared before but I confirmed that your fix works.