Crash when loading session including params file

1. Load a PDB that includes a ligand, along with appropriate params file.

2. Save session.

3. Restart client and attempt to load saved session.

4. Crash with output:

ERROR: unrecognized aa type 
ERROR:: Exit from: /Users/folditbuilder/foldit/rosetta-interactive/source/src/core/chemical/AA.cc line: 292