Fix crash when no molecular orbitals loaded

Check that m_numMOs is non-zero, return early if it is. This fixes a
crash with the GAMESS reader when loading log files that aborted.

Change-Id: Idf5e98794b41be3187fc0731ee071f0faaa02ec9
Merge topic 'gaussian-check' into master

4326221a Fix crash when no molecular orbitals loaded