windows opengl: When the 2nd param is NULL, the 1st is ignored anyway.

Change-Id: I840e8bb2d2ccae869c330bb32dba484b4a835a51
Reviewed-on: https://gerrit.libreoffice.org/18248Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

vcl/source/opengl/OpenGLContext.cxx

@@ -1296,7 +1296,7 @@ void OpenGLContext::reset()
         if (itr != g_vShareList.end())
             g_vShareList.erase(itr);
 
-        wglMakeCurrent( m_aGLWin.hDC, 0 );
+        wglMakeCurrent(NULL, NULL);
         wglDeleteContext( m_aGLWin.hRC );
         ReleaseDC( m_aGLWin.hWnd, m_aGLWin.hDC );
     }
@@ -1473,7 +1473,7 @@ void OpenGLContext::resetCurrent()
     OpenGLZone aZone;
 
 #if defined( WNT )
-    wglMakeCurrent( m_aGLWin.hDC, 0 );
+    wglMakeCurrent(NULL, NULL);
 #elif defined( MACOSX )
     (void) this; // loplugin:staticmethods
     OpenGLWrapper::resetCurrent();