total_primary_dither_positions is a string in some cases

[bhilbert4]

When running the yaml_generator on an observation with certain primary dither patterns (e.g. 8NIRSPEC), the total_primary_dither_positions entry of the yaml file contains the entire string, rather than just the relevant integer. I'm not sure how this is happening, since there is a clause in the APR reader (in read_generic_imaging_observation) that should be stripping the letters away.

Seen in program 1073.