manager: avoid deep nesting

Use an early return rather than deep nesting to improve the
code legibility.

https://bugzilla.gnome.org/show_bug.cgi?id=764623

src/gcal-manager.c

@@ -340,13 +340,11 @@ on_client_connected (GObject      *source_object,
                      GAsyncResult *result,
                      gpointer      user_data)
 {
+  GcalManagerUnit *unit;
   GcalManager *manager;
   ECalClient *client;
-  GError *error;
-
   ESource *source;
-
+  GError *error;
-  GcalManagerUnit *unit;
 
   manager = GCAL_MANAGER (user_data);
   source = e_client_get_source (E_CLIENT (source_object));
@@ -357,8 +355,20 @@ on_client_connected (GObject      *source_object,
 
   error = NULL;
   client = E_CAL_CLIENT (e_cal_client_connect_finish (result, &error));
-  if (error == NULL)
+
+  if (error)
     {
+      remove_source (GCAL_MANAGER (user_data), source);
+      g_warning ("%s: Failed to open/connect '%s': %s",
+                 G_STRFUNC,
+                 e_source_get_display_name (source),
+                 error->message);
+
+      g_object_unref (source);
+      g_error_free (error);
+      return;
+    }
+
   unit = g_new0 (GcalManagerUnit, 1);
   unit->connected = TRUE;
   unit->client = g_object_ref (client);
@@ -396,20 +406,6 @@ on_client_connected (GObject      *source_object,
 
   g_clear_object (&client);
 }
-  else
-    {
-      /* in any other case, remove it*/
-      remove_source (GCAL_MANAGER (user_data), source);
-      g_warning ("%s: Failed to open/connect '%s': %s",
-                 G_STRFUNC,
-                 e_source_get_display_name (source),
-                 error->message);
-
-      g_object_unref (source);
-      g_error_free (error);
-      return;
-    }
-}
 
 static void
 on_client_readonly_changed (EClient    *client,