codegen.py fix: missing of some values to communicate

In the function comm_directions sides were missing in the communication.

pystencils_walberla/codegen.py

@@ -352,3 +352,10 @@ def comm_directions(direction):
             dir_as_list[i] = 0
             if not all(e == 0 for e in dir_as_list):
                 yield tuple(dir_as_list)
+    # in the 3D case also the sides have to be added
+    if len(direction) == 3:
+        for i in range(len(direction)):
+            dir_as_list = [0, 0, 0]
+            dir_as_list[i] = direction[i]
+            if not all(e == 0 for e in dir_as_list):
+                yield tuple(dir_as_list)