pyscamp.selfjoin returns zero vector if m=3

[keichi]

Describe the bug
pyscamp.selfjoin returns a zero vector if m=3. If m>= 4 the results are correct.

To Reproduce

x = np.random.rand(10)
pyscamp.selfjoin(x, m=3)

gives a zero vector like this:

(array([0., 0., 0., 0., 0., 0., 0., 0.], dtype=float32),
 array([0, 1, 2, 3, 4, 5, 6, 7], dtype=int32))

stumpy gives correct results:

stumpy.stump(x, m=3)

mparray([[0.543935636387785, 4, -1, 4],
         [0.6665659559814567, 5, -1, 5],
         [0.29289592419909743, 7, 0, 7],
         [1.5383853098049423, 1, 1, 6],
         [0.543935636387785, 0, 0, 7],
         [0.6665659559814567, 1, 1, 7],
         [0.6135462405979734, 2, 2, -1],
         [0.29289592419909743, 2, 2, -1]], dtype=object)

Outputs of pyscamp.selfjoin and stumpy.stump are identical if m>=4.

Expected behavior
Output of pyscamp.selfjoin should match stumpy.stump.

System Information

• OS: Rocky Linux 8.10
• System Architecture: x86_64
• Package and Version: pyscamp 4.0.1 installed from source using pip