Silence unsigned/signed comparison

valid since row was tested to be positive earlier
lightwood-roller/liblightwood-roller.c:1455:27: warning:
comparison between signed and unsigned integer expressions [-Wsign-compare]
       if (row == 0 || row == thornbury_model_get_n_rows (priv->model))

Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Reviewed-by: Andrew Shadura <andrew.shadura@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D6347

src/lightwood-roller/liblightwood-roller.c

@@ -1452,7 +1452,7 @@ release_event (ClutterActor *actor,
 
     /* when row returned is 0 or the max value in the model,
      * then it is always first row in the roller */
-      if (row == 0 || row == thornbury_model_get_n_rows (priv->model))
+      if (row == 0 || row == (int)thornbury_model_get_n_rows (priv->model))
         row = 0;
 
       if (priv->glow == TRUE)