[gnome-calendar] quick-add-popover: Only remove existing rows

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 09b986f526e2c67c5b457f3599640511c8f90d0a
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sun Jan 28 12:45:57 2018 -0200

    quick-add-popover: Only remove existing rows
    
    We can receive the source-changed signal on read-only sources,
    and these sources have no row associated. Trying to remove the
    non-existing row would yield a warning.

 src/gcal-quick-add-popover.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/gcal-quick-add-popover.c b/src/gcal-quick-add-popover.c
index 093f8156..f5fd7ada 100644
--- a/src/gcal-quick-add-popover.c
+++ b/src/gcal-quick-add-popover.c
@@ -536,7 +536,9 @@ on_source_changed (GcalManager         *manager,
   /* If the calendar changed from/to read-only, we add or remove it here */
   if (!gcal_manager_is_client_writable (self->manager, source))
     {
-      gtk_container_remove (GTK_CONTAINER (self->calendars_listbox), row);
+      if (row)
+        gtk_container_remove (GTK_CONTAINER (self->calendars_listbox), row);
+
       return;
     }
   else if (!row)