Fix xcopy problem

Seems to work differently on appveyor build

src/VideoStreaming/VideoStreaming.pri

@@ -69,7 +69,8 @@ LinuxBuild {
         QMAKE_POST_LINK += xcopy \"$$GST_ROOT_WIN\\bin\*.\" \"$$DESTDIR_WIN\" /S/Y $$escape_expand(\\n)
 
         # Copy GStreamer plugins
-        QMAKE_POST_LINK += $$escape_expand(\\n) xcopy \"$$GST_ROOT_WIN\\lib\\gstreamer-1.0\\*.dll\" \"$$DESTDIR_WIN\\gstreamer-plugins\\\" /S/Y $$escape_expand(\\n)
+        QMAKE_POST_LINK += $$escape_expand(\\n) xcopy \"$$GST_ROOT_WIN\\lib\\gstreamer-1.0\\*.dll\" \"$$DESTDIR_WIN\\gstreamer-plugins\\\" /Y $$escape_expand(\\n)
+        QMAKE_POST_LINK += $$escape_expand(\\n) xcopy \"$$GST_ROOT_WIN\\lib\\gstreamer-1.0\\validate\\*.dll\" \"$$DESTDIR_WIN\\gstreamer-plugins\\validate\\\" /Y $$escape_expand(\\n)
     }
 } else:AndroidBuild {
     #- gstreamer assumed to be installed in $$PWD/../../android/gstreamer-1.0-android-armv7-1.5.2