Enable hiding OSK on Windows

src/frameworks/UBPlatformUtils_win.cpp

@@ -439,11 +439,19 @@ void UBPlatformUtils::showFullScreen(QWidget *pWidget)
 
 void UBPlatformUtils::showOSK(bool show)
 {
-    Q_UNUSED(show);
-
+    if (show) {
         QString windir = qgetenv("WINDIR");
         QString osk_path = windir+"\\System32\\osk.exe";
 
-    QProcess newProcess;
-    newProcess.startDetached("explorer.exe", QStringList() << osk_path);
+        QProcess oskProcess;
+        // We have to pass by explorer.exe because osk.exe can only be launched
+        // directly with administrator rights
+        oskProcess.startDetached("explorer.exe", QStringList() << osk_path);
+    }
+
+    else {
+        HWND oskWindow = ::FindWindow(TEXT("OSKMainClass"), NULL);
+        if (oskWindow)
+            PostMessage(oskWindow, WM_SYSCOMMAND, SC_CLOSE, 0);
+    }
 }