bus-message: let's always use -EBADMSG when the message is bad

-EINVAL means the arguments were somehow wrong, so translate the code we get
internally into -EBADMSG when returning.

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

@@ -5385,6 +5385,8 @@ int bus_message_parse_fields(sd_bus_message *m) {
                                 &m->root_container.item_size,
                                 &m->root_container.offsets,
                                 &m->root_container.n_offsets);
+                if (r == -EINVAL)
+                        return -EBADMSG;
                 if (r < 0)
                         return r;
         }