fix dirac for older MATLAB versions
fix dirac for older MATLAB versions

paulstapor/AMICI,AMICI-developer/AMICI,AMICI-developer/AMICI,paulstapor/AMICI,FFroehlich/AMICI,FFroehlich/AMICI,AMICI-developer/AMICI,FFroehlich/AMICI,paulstapor/AMICI,paulstapor/AMICI,AMICI-developer/AMICI,FFroehlich/AMICI