sd-bus: drop redundant code

If c->item_size is 0, the next item to parse in a structure is empty.
However, this also implies that the signature must be empty. The latter
case is already handled just fine by enter_struct_or_dict_entry() so
there is no reason to handle the same case in the caller.

src/libsystemd/sd-bus/bus-message.c

@@ -3954,12 +3954,6 @@ static int enter_struct_or_dict_entry(
                 if (r < 0)
                         return r;
 
-        } else if (c->item_size <= 0) {
-
-                /* gvariant empty struct */
-                *item_size = 0;
-                *offsets = NULL;
-                *n_offsets = 0;
         } else
                 /* gvariant with contents */
                 return build_struct_offsets(m, contents, c->item_size, item_size, offsets, n_offsets);