fixes issue with 'stuck' mono panners (when using a stereo
monitoring section and auto-connect): the send to monitor
section is added after the main panner. At this point the
channel-count is different, but the send shared panner() with
the main route.
Here: mono-panner on track, stereo-panner; and they shared control
settings. since stereo-panner's width is 1, the position cannot be
changed.
7bc3e0dab4