Fix Coverity CID 649243 (DIVIDE_BY_ZERO) by validating sweep step
values before calculating 2D sweep dimensions.
Move sweep step validation to on_startStop_clicked() so invalid sweep
configurations are reported to the user before a sweep begins. Display
an error message when either sweep step is zero and prevent the sweep
from starting.
Retain defensive validation when updating 2D sweep settings to guard
against invalid configurations received from saved settings or other
code paths.
Signed-off-by: Robin Getz <rgetz503@gmail.com>
Robin Getz
382d541eae