missing cairo_surface_destroy

Change-Id: I4ff8dcf928ebefed1eaeebdcdcfb90c56ddfd39e
Reviewed-on: https://gerrit.libreoffice.org/67440
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/headless/svpgdi.cxx

@@ -1628,6 +1628,7 @@ void SvpSalGraphics::drawBitmap(const SalTwoRect& rTR, const BitmapBuffer* pBuff
 {
     cairo_surface_t* source = createCairoSurface( pBuffer );
     copyWithOperator(rTR, source, eOp);
+    cairo_surface_destroy(source);
 }
 
 void SvpSalGraphics::drawBitmap( const SalTwoRect& rTR,