fix #735.  The rhs of the ode is now not evaluated for negative values if the current value is not negative
fix #735.  The rhs of the ode is now not evaluated for negative values if the current value is not negative

jonasfoe/COPASI,copasi/COPASI,jonasfoe/COPASI,jonasfoe/COPASI,copasi/COPASI,copasi/COPASI,jonasfoe/COPASI,copasi/COPASI,copasi/COPASI,jonasfoe/COPASI,jonasfoe/COPASI,jonasfoe/COPASI,copasi/COPASI,copasi/COPASI,copasi/COPASI,jonasfoe/COPASI,copasi/COPASI,jonasfoe/COPASI