Fix "Selected time in notstrictly monotonic" error when loading csv

Problem:

It is a fix for https://github.com/facontidavide/PlotJuggler/issues/61

The first time I load a csv file to PlotJuggler there is a pop-up asking to select the time axis. The file is loaded correctly. When I want to load another file with same data structure, there is "Selected time in notstrictly monotonic" error.

The only way I can get data to be loaded correctly then, is to change the name of time axis in the csv.

Fix:

The cause of a problem was a wrong index to the time axis when loading a second file.