ISIViolations can be imaginary

[RoddyMGrieves]

I think the ISIViolations.m function can still output imaginary values.

From Llobet et al. 2022 (pp 11): "The equations for C and C' may not have a real solution if nv is large; this can arise if the activities of reference and contaminant spikes are strongly correlated, thus causing a departure from the assumption of independent firing, and/or as a result of stochastic variations. In such cases - almost invariably removed by a quality threshold - we simply follow the convention of setting C = 1."

I have observed imaginary values for fpRate, even though the comments at the top of the code say that the expression no longer returns imaginary values.

I suggest adding:

if ~isreal(fpRate)
    fpRate = 1;
end