[gtkmm] Gdk::TimeCoord: Fix copy and move assignment

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 8b5cd8e3fbce7f8dfa4bdc6f51efdff647abad24
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Wed Jul 26 10:42:05 2017 +0200

    Gdk::TimeCoord: Fix copy and move assignment
    
    Use the technique with a temporary object and swap(). It's easy and safe,
    and it handles self assignment.

 gdk/src/timecoord.ccg |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)
---
diff --git a/gdk/src/timecoord.ccg b/gdk/src/timecoord.ccg
index d90b43c..b25464c 100644
--- a/gdk/src/timecoord.ccg
+++ b/gdk/src/timecoord.ccg
@@ -16,6 +16,7 @@
  */
 
 #include <gdk/gdk.h>
+#include <utility> // std::move(), std::swap()
 
 namespace
 {
@@ -43,8 +44,8 @@ TimeCoord::TimeCoord(const TimeCoord& other)
 
 TimeCoord& TimeCoord::operator=(const TimeCoord& other)
 {
-  g_free(gobject_);
-  gobject_ = time_coord_copy(other.gobject_);
+  TimeCoord temp(other);
+  std::swap(gobject_, temp.gobject_);
   return *this;
 }
 
@@ -57,9 +58,8 @@ TimeCoord::TimeCoord(TimeCoord&& other) noexcept
 
 TimeCoord& TimeCoord::operator=(TimeCoord&& other) noexcept
 {
-  g_free(gobject_);
-  gobject_ = std::move(other.gobject_);
-  other.gobject_ = nullptr;
+  TimeCoord temp(std::move(other));
+  std::swap(gobject_, temp.gobject_);
   return *this;
 }