Fix extend-with-overflow

[charlesbmi]

Previous behavior:

>>> import numpy as np
>>> from numpy_ringbuffer import RingBuffer
>>> r = RingBuffer(5)
>>> r.extend(np.arange(8))
>>> r
<RingBuffer of array([], dtype=float64)>

Expected/fixed behavior:

>>> import numpy as np
>>> from numpy_ringbuffer import RingBuffer
>>> r = RingBuffer(5)
>>> r.extend(np.arange(8))
>>> r
<RingBuffer of array([3., 4., 5., 6., 7.])>

[eric-wieser]

Thanks for catching this! Unfortunately CI seems to be failing, but that might be because I've not looked at this project for years.

[charlesbmi]

You're welcome! I added a separate PR that I think might fix the workflow: #19 , although I could only test it locally.