Nil Pointer Crash when Initializing Snowflake Proxy

https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/blob/main/proxy/lib/snowflake.go#L568

Line 568 ought to be moved below 589 - if the event dispatcher isn't set the proxy will crash. I came across this bumping snowflake to the the latest release in Orbot via our IPtProxy wrapper library.

https://github.com/tladesignz/IPtProxy/issues/39

For now, we simply just init'd our own event dispatcher instance to sidestep the crash.