Debug false lines in extracted spectra

PIPE1D-14 identifies some false lines in coadded spectra from the integration test. They appear to be coming from negative features in the sky spectra. In particular, visit=25 arm=r has a single pixel in the fiberTrace at row=116 for the eighth spectrum, which is producing a 3-sigma negative value in the extracted spectrum, but inspection of the calExp shows that pixel flux value is well within the expected noise.