[gnome-calendar/gnome-3-36] calendar-monitor: fix unused variable warning

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

commit 0084a5975edcae6ec5ed1ce13596f398207bf862
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Wed Apr 1 20:30:06 2020 -0500

    calendar-monitor: fix unused variable warning
    
    Fixes:
    
    [43/52] Compiling C object 'src/25a6634@@gcal-private@sta/core_gcal-calendar-monitor.c.o'
    ../../../../Projects/gnome-calendar/src/core/gcal-calendar-monitor.c: In function 
‘on_client_view_objects_added_cb’:
    ../../../../Projects/gnome-calendar/src/core/gcal-calendar-monitor.c:402:16: warning: variable ‘old_size’ 
set but not used [-Wunused-but-set-variable]
      402 |           gint old_size;
          |                ^~~~~~~~

 src/core/gcal-calendar-monitor.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/src/core/gcal-calendar-monitor.c b/src/core/gcal-calendar-monitor.c
index 0a704f13..87172e78 100644
--- a/src/core/gcal-calendar-monitor.c
+++ b/src/core/gcal-calendar-monitor.c
@@ -399,7 +399,9 @@ on_client_view_objects_added_cb (ECalClientView      *view,
         {
           GenerateRecurrencesData recurrences_data;
           ICalComponent *icomponent;
+#if GCAL_ENABLE_TRACE
           gint old_size;
+#endif
 
           if (g_cancellable_is_cancelled (self->cancellable))
             return;
@@ -409,7 +411,10 @@ on_client_view_objects_added_cb (ECalClientView      *view,
           recurrences_data.monitor = self;
           recurrences_data.expanded_events = expanded_events;
 
+#if GCAL_ENABLE_TRACE
           old_size = expanded_events->len;
+#endif
+
           e_cal_client_generate_instances_for_object_sync (client,
                                                            icomponent,
                                                            range_start_time,