Rewind message before parsing it in SdBusMessage.get_contents

The same message can be given to multiple handlers for example
in case of multiple tasks awaiting on signals.

This would cause the "Dbus type '\x00' is unknown" errors.

src/sdbus/sd_bus_internals_message.c

@@ -955,7 +955,7 @@ static PyObject* iter_tuple_or_single(_Parse_state* parser) {
 }
 
 static PyObject* SdBusMessage_get_contents2(SdBusMessageObject* self, PyObject* Py_UNUSED(args)) {
-        const char* message_signature = sd_bus_message_get_signature(self->message_ref, 0);
+        const char* message_signature = sd_bus_message_get_signature(self->message_ref, 1);
 
         if (message_signature == NULL) {
                 PyErr_SetString(PyExc_TypeError, "Failed to get message signature.");
@@ -966,6 +966,7 @@ static PyObject* SdBusMessage_get_contents2(SdBusMessageObject* self, PyObject*
                 Py_RETURN_NONE;
         }
 
+        CALL_SD_BUS_AND_CHECK(sd_bus_message_rewind(self->message_ref, 1));
         _Parse_state read_parser = {
             .message = self->message_ref,
             .container_char_ptr = message_signature,

test/test_read_write_dbus_types.py

@@ -429,6 +429,14 @@ class TestEnum(str, Enum):
 
         self.assertEqual(message.get_contents(), TestEnum.SOMETHING)
 
+    def test_reading_multiple_times(self) -> None:
+        message = create_message(self.bus)
+        message.append_data('s', 'test')
+        message.seal()
+
+        for _ in range(5):
+            message.get_contents()
+
 
 if __name__ == "__main__":
     main()