ADC frequency: markers don't disappear from the plot when disabled.

[AlexandraTrifan]

Environment:

• OS: Debian 13 arm64
• N/A
• a3a7c43

Describe the bug
The marker count doesn't always apply as expected when the plot is stopped. Several times, the markers
count is applied only when changing the marker type. The markers don't disappear from the plot when
the Marker Panel and the Marker Channel Settings are disabled.

To Reproduce
Steps to reproduce the behavior:

1. Go to ADC Frequency instrument and Run a continuous capture.
2. Enable the Marker Panel from the bottom right Measure button and the Marker settings from the channel menu.
3. Set type to PEAK and count to 5. Start /stop the instrument.
4. Modify the count to 8 and start the instrument.
5. The marker count is not applied on the plot.
6. Modify the type to Fixed and the Count to 6.
7. The Plot is no longer in sync with the Marker settings.
8. Disable the Marker setting; the markers don't disappear from the plot.

Expected behavior
Marker behaviour is not constant and as expected.

Screenshots
Additional context

[SeptimiuVana]

Also set min number of singletone markers to 2. The computation algorithm requires at least 2 markers.
This was causing a segmentation fault.