fix softmax masking

Author: younesStrittmatter

psyneulink/core/components/functions/nonstateful/transferfunctions.py

@@ -3162,7 +3162,8 @@ def apply_softmax(self, input_value, gain, mask_threshold, output_type):
             v = np.where(np.abs(v) > mask_threshold, v, -np.inf)
 
         # Make numerically stable by shifting by max value
-        v = v - np.max(v)
+        if np.any(v != -np.inf):
+            v = v - np.max(v)
 
         # Exponentiate
         v = np.exp(v)

tests/composition/test_emcomposition.py

@@ -778,7 +778,7 @@ def test_assign_field_weights_and_0_vs_None(self,
         # Note: field_weights favors A
         if softmax_choice == pnl.MAX_VAL:
             if operation == pnl.L0:
-                expected = [[1.703812], [0.], [3.407624]]
+                expected = [[1.467373], [0.], [2.934746]]
             else:
                 expected = [[1.419423, 0.0], [0.0, 1.419423], [2.838846, 2.838846]]
         else: