missing cairo_surface_destroy

Change-Id: I4ff8dcf928ebefed1eaeebdcdcfb90c56ddfd39e
Reviewed-on: https://gerrit.libreoffice.org/67451
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
diff --git a/vcl/headless/svpgdi.cxx b/vcl/headless/svpgdi.cxx
index 1c310a2..502aa43 100644
--- a/vcl/headless/svpgdi.cxx
+++ b/vcl/headless/svpgdi.cxx
@@ -1630,6 +1630,7 @@ void SvpSalGraphics::drawBitmap(const SalTwoRect& rTR, BitmapBuffer* pBuffer, ca
{
    cairo_surface_t* source = createCairoSurface( pBuffer );
    copyWithOperator(rTR, source, eOp);
    cairo_surface_destroy(source);
}

void SvpSalGraphics::drawBitmap( const SalTwoRect& rTR,