Eliminated numpy log(0) error message when writing bond potentials, which is...

Eliminated numpy log(0) error message when writing bond potentials, which is caught anyway by .isnan

mrdna/model/nonbonded.py

@@ -153,7 +153,8 @@ class HarmonicBond(HarmonicPotential):
     def potential(self,dr):
         u = HarmonicPotential.potential(self,dr)
         if self.correct_geometry:
-            du = 2*0.58622592*np.log(dr+self.r0) * self.temperature/295
+            with np.errstate(divide='ignore',invalid='ignore'):
+                du = 2*0.58622592*np.log(dr+self.r0) * self.temperature/295
             du[np.logical_not(np.isfinite(du))] = 0
             u = u-du
         return u