Fixed a bug that prevented reading DSSP 2.0.4 files (and maybe others.)

Code would crash at around this line in a DSSP output file:

  #  RESIDUE AA STRUCTURE BP1 BP2  ACC     N-H-->O    O-->H-N    N-H-->O    O-->H-N    TCO  KAPPA ALPHA  PHI   PSI    X-CA   Y-CA   Z-CA 

Which is where it's supposed to begin parsing. I added a small short-circuit conditional to prevent that.
Other bugs may linger.