flacenc: remove single entry if from loop
flacenc: remove single entry if from loop

Iterate from the 2nd channel on and create the 1 channel struct
outside to make loop structure simpler and only slightly faster.

hizukiayaka/gst-plugins-good,rawoul/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good,hizukiayaka/gst-plugins-good,StreamUtils/gst-plugins-good,sebras/gst-plugins-good,GrokImageCompression/gst-plugins-good,GrokImageCompression/gst-plugins-good,rawoul/gst-plugins-good,hizukiayaka/gst-plugins-good,pexip/gst-plugins-good,Kurento/gst-plugins-good,pexip/gst-plugins-good,sebras/gst-plugins-good,GStreamer/gst-plugins-good,stfl/gst-plugins-good,StreamUtils/gst-plugins-good,Kurento/gst-plugins-good,rawoul/gst-plugins-good,pexip/gst-plugins-good,Kurento/gst-plugins-good,GrokImageCompression/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,GrokImageCompression/gst-plugins-good,Kurento/gst-plugins-good,hizukiayaka/gst-plugins-good,stfl/gst-plugins-good,Kurento/gst-plugins-good,sebras/gst-plugins-good,pexip/gst-plugins-good,StreamUtils/gst-plugins-good,StreamUtils/gst-plugins-good,sebras/gst-plugins-good,rawoul/gst-plugins-good