2D: don't use np.empty as a small random number generator

adaptive/learner.py

@@ -724,7 +724,7 @@ class Learner2D(BaseLearner):
                 # It is important not to return exact zeros because
                 # otherwise the algo will try to add the same point
                 # to the stack each time.
-                ip_real = lambda x: np.empty(len(x))
+                ip_real = lambda x: np.random.rand(len(x)) * 1e-15
             n_interp = list(self._interp.values())
             values = ip_real(p[n_interp])
             for n, value in zip(n_interp, values):