views/month: Hide invisible rows

Change the child-visible property of rows when allocating. It's safe
to do in allocation because it doesn't affect layout, just rendering.

Related:
https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/402

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/659>

src/gui/views/gcal-month-view.c

@@ -1445,6 +1445,7 @@ gcal_month_view_size_allocate (GtkWidget *widget,
     {
       GtkAllocation row_allocation;
       GtkWidget *row;
+      gboolean child_visible;
 
       row = g_ptr_array_index (self->week_rows, i);
 
@@ -1457,6 +1458,9 @@ gcal_month_view_size_allocate (GtkWidget *widget,
 
 #undef ROW_Y
 
+      child_visible = (row_allocation.y + row_allocation.height > header_height) && row_allocation.y < height;
+      gtk_widget_set_child_visible (row, child_visible);
+
       gtk_widget_size_allocate (row, &row_allocation, baseline);
     }