CSV import: don't choke on files with header rows at start

[azonenberg]

CSV files imported from the Digilent Analog Discover don't work right.

Example file format:

`
#Digilent WaveForms Oscilloscope Acquisition
#Device Name: ADP3450
#Serial Number: SN:210018B04985
#Date Time: 2021-04-14 13:10:34.255.812.740

Time (s),Channel 1 (V)
-0.000130832912,-0.01202555057749403
`