Missing DSSAT failure mode(s)

[frostbytten]

There are times when DSSAT fails but does not exit with an invalid return code or write to the fort.0 file. This gives the user a false sense that simulations completed. We should check for the presence of a fort.0 file prior to marking a simulation as complete. This could lead to the opposite problem of a warning being thrown, which is NOT an error and the user being informed of an error. This is probably better for the end user.