added check for numTrueCh if matrix is of size 0 to avoid dividing by 0 -- cov175338
added check for numTrueCh if matrix is of size 0 to avoid dividing by 0 -- cov175338

LorenzE/mne-cpp,mne-tools/mne-cpp,mne-tools/mne-cpp,LorenzE/mne-cpp,mne-tools/mne-cpp,mne-tools/mne-cpp,chdinh/mne-cpp,mne-tools/mne-cpp,chdinh/mne-cpp,chdinh/mne-cpp,mne-tools/mne-cpp,chdinh/mne-cpp,LorenzE/mne-cpp,chdinh/mne-cpp,chdinh/mne-cpp,LorenzE/mne-cpp