Communication error could be salvaged in some cases #46
Description
Currently if there is a persistent communication breakdown in plotLineAndTime which ends up returning a null from ebb_motion.QueryPRGButton(self.serialPort), then python aborts the plot with a runtime error message. This loses position reference for the plot, and thus the entire plot is ruined.
The suggested change incorporated in the attached file explicitly looks for a null response. Here if a null response occurs, the program substitutes a simulated push of the pause button. Therefore the user may be able to use the "Resume" to rescue the plot, after fixing the communication problem.
The attached file is built from a base of the proposed fix for issue 45.