revid: Duplicate sender routines created

[Alan Noble]

Under some circumstances revid creates duplicate go routines for senders. Once a sender is duplicated, it is never reclaimed, resulting in associated resources never being freed.

One such circumstance is operator error, reproducible as follows:

• Set Output to Rtmp
• Set mode to Http (instead of Normal or Paused)

This results in two RTMP senders.

[Saxon Milton]

Addressed in PR #251

[Saxon Milton]

Addressed in PR #251