Merge remote-tracking branch 'origin/5.4' into 5.5v5.5.0-beta1

Change-Id: Ic1f50d8d646e53f6a5629db98fcaa7a1a99d8b4f

1 files changed, 6 insertions, 2 deletions

diff --git a/src/winextras/qwintaskbarbutton.cpp b/src/winextras/qwintaskbarbutton.cpp
index f0be30a..7150e1b 100644
--- a/src/winextras/qwintaskbarbutton.cpp
+++ b/src/winextras/qwintaskbarbutton.cpp
@@ -54,7 +54,7 @@ QT_BEGIN_NAMESPACE
     \class QWinTaskbarButton
     \inmodule QtWinExtras
     \brief The QWinTaskbarButton class represents the Windows taskbar button for
-    a window.
+    a top-level window (Windows 7 and newer).
 
     \since 5.2
 
@@ -71,6 +71,9 @@ QT_BEGIN_NAMESPACE
 
     \snippet code/taskbar.cpp taskbar_cpp
 
+    \note The class wraps API only available since Windows 7. Instantiating it
+    on Windows XP or Windows Vista causes a runtime warning.
+
     \sa QWinTaskbarProgress
  */
 
@@ -104,7 +107,8 @@ QWinTaskbarButtonPrivate::QWinTaskbarButtonPrivate() : progressBar(0), pTbList(0
 
 QWinTaskbarButtonPrivate::~QWinTaskbarButtonPrivate()
 {
-    pTbList->Release();
+    if (pTbList)
+        pTbList->Release();
 }
 
 HWND QWinTaskbarButtonPrivate::handle()