v.category: print message about added centroids only when at least one has been added to the map

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@51094 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.category/main.c

@@ -325,7 +325,8 @@ int main(int argc, char *argv[])
 		Vect_write_line(&Out, GV_CENTROID, Points, Cats);
 		new_centr++;
 	    }
-	    G_message(_("%d new centroids placed in output map"), new_centr);
+	    if (new_centr > 0) 
+		G_message(_("%d new centroids placed in output map"), new_centr);
 	}
 	break;