Merge branch 'fixing_nan' into 'NIFTy_5'

Fixing NaNs in PoissonEnergy

See merge request !321

nifty5/operators/energy_operators.py

@@ -191,7 +191,12 @@ class PoissonianEnergy(EnergyOperator):
 
     def apply(self, x):
         self._check_input(x)
-        res = x.sum() - x.log().vdot(self._d)
+        res = x.sum()
+        tmp = res.val.local_data if isinstance(res, Linearization) else res
+        # if we have no infinity here, we can continue with the calculation;
+        # otherwise we know that the result must also be infinity
+        if not np.isinf(tmp):
+            res = res - x.log().vdot(self._d)
         if not isinstance(x, Linearization):
             return Field.scalar(res)
         if not x.want_metric: