Attempt to fix scope trigger

[srcejon]

This is a possible fix for #1901, but please review

Currently, the code in processTrace only ever appears to look at the first sample in a block of data

const Complex& s = *vbegin[triggerStreamIndex];

I'm guessing it needs to be indexed using processed (as that variable isn't read anywhere else in the loop)

const Complex& s = vbegin[triggerStreamIndex][processed];

And it seems to trigger more as I'd expect.

[f4exb]

This seems to make sense