Fixing the mis-interpreted bad slope flag.

This fix was developed Pasha and approved by the Data Analysis Working Group (DAWG) and recorded as Task#2 on the DAWG webpage.

https://homepage.usask.ca/~pbp672/Data_Analysis_WG_Task2_Bad_phase_flag.pdf

Note: We replaced a bad slope flag value of 9999 by the negative phase fitting error.