[glibmm] ConstructParams: Do not increment allocation size twice

[Daniel Elstner <daniel src gnome org>]

commit a84268368307e97d50c8c1ce33dd1d58cf2866d3
Author: Daniel Elstner <daniel kitta gmail com>
Date:   Tue May 9 20:10:39 2017 +0200

    ConstructParams: Do not increment allocation size twice

 glib/glibmm/object.cc |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/glib/glibmm/object.cc b/glib/glibmm/object.cc
index 58166b7..ce14269 100644
--- a/glib/glibmm/object.cc
+++ b/glib/glibmm/object.cc
@@ -71,8 +71,9 @@ ConstructParams::ConstructParams(
     }
 
     if (n_parameters >= n_alloced_params) {
-      parameter_names = g_renew(const char*, parameter_names, n_alloced_params += 8);
-      parameter_values = g_renew(GValue, parameter_values, n_alloced_params += 8);
+      n_alloced_params += 8;
+      parameter_names = g_renew(const char*, parameter_names, n_alloced_params);
+      parameter_values = g_renew(GValue, parameter_values, n_alloced_params);
     }
 
     auto& param_name = parameter_names[n_parameters];