Fix the bug that GOMC could not read the PDB and PSF file for system that has only 1 molecule
Fix the bug that GOMC could not read the PDB and PSF file for system that has only 1 molecule

GOMC-WSU/GOMC_Serial,GOMC-WSU/GOMC,GOMC-WSU/GOMC,GOMC-WSU/GOMC,GOMC-WSU/GOMC,GOMC-WSU/GOMC_Serial,GOMC-WSU/GOMC,GOMC-WSU/GOMC_Serial