Tolerate failures in opening listeners

Quoting from https://blog.torproject.org/blog/combined-flash-proxy-pyobfsproxy-browser-bundles#comment-18784.

In China, I tested flashproxy in XP sp3 and WIN7 network environment of ADSL+router. Flashproxy can fetch new bridge in WIN7, but the new bridge is very slow. In XP sp3, flshproxy can not work. In task manager, flashproxy-client.exe appears for only seconds, flashproxy-reg-email.exe and flashproxy-reg-http.exe never appear.

I wonder if any uPNP configuration problem happens in my XP sp3 system.