add missing type conversion in image_molecules before calling the C code (#1466)
add missing type conversion in image_molecules before calling the C code (#1466)


mdtraj/mdtraj,rmcgibbo/mdtraj,rmcgibbo/mdtraj,gph82/mdtraj,dwhswenson/mdtraj,mdtraj/mdtraj,mattwthompson/mdtraj,mdtraj/mdtraj,gph82/mdtraj,mattwthompson/mdtraj,dwhswenson/mdtraj,mattwthompson/mdtraj,dwhswenson/mdtraj,gph82/mdtraj,rmcgibbo/mdtraj,mattwthompson/mdtraj