double-flat-field + filtering crashes when data has negative values

In a recent ID19 acquisition, the last projections are empty, in the sense that the sample is completely outside FoV. May be the shutter was even closed before the end of acquisition ? Regardless, some pixels are such that projection < dark or flat < dark (!), which yields negative values after flat-field. The gaussian high-pass filtering occurring after double-flat-field chokes on these values, and all the reconstruction is messed up.