Spinner range fix (for #250)

[pl0xz0rz]

This PR fixes a bug with spinner range widgets where the callback updating the view isn't called, introduced in #250

[miranov25]

Real case was OK, tests OK - mrging

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
------------------------------------------------------------------------------------------------ JSON report -------------------------------------------------------------------------------------------------
report saved to: test6.json
====================================================================================== 37 passed, 7 warnings in 54.62s =======================================================================================

real    0m56.109s
user    11m11.644s
sys     0m39.556s