level: Don't read over the end of the input memory
level: Don't read over the end of the input memory

Previously we advanced the in_data pointer by bps for every channel, and then
later again for block_size*bps. This caused us to be one sample further than
expected if an input buffer covered two analysis frames. And in the end lead
to completely bogus values reported by level.

https://bugzilla.gnome.org/show_bug.cgi?id=746065

hizukiayaka/gst-plugins-good,sebras/gst-plugins-good,vatavuserban/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,ikonst/gst-plugins-good,loshca/gst-plugins-good,sh0/gst-plugins-good,pexip/gst-plugins-good,StreamUtils/gst-plugins-good,rawoul/gst-plugins-good,shelsonjava/gst-plugins-good,Kurento/gst-plugins-good,loshca/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,froggatt/gst-plugins-good-m,BigBrother-International/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,stfl/gst-plugins-good,pexip/gst-plugins-good,chamois94/gst-plugins-good,GStreamer/gst-plugins-good,veo-labs/gst-plugins-good,rawoul/gst-plugins-good,stfl/gst-plugins-good,GrokImageCompression/gst-plugins-good,kittee/gst-plugins-good,loshca/gst-plugins-good,kittee/gst-plugins-good,BigBrother-International/gst-plugins-good,StreamUtils/gst-plugins-good,ikonst/gst-plugins-good,chamois94/gst-plugins-good,ikonst/gst-plugins-good,sh0/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,froggatt/gst-plugins-good-m,StreamUtils/gst-plugins-good,Kurento/gst-plugins-good,veo-labs/gst-plugins-good,hizukiayaka/gst-plugins-good,GStreamer/gst-plugins-good,vatavuserban/gst-plugins-good,GrokImageCompression/gst-plugins-good,sh0/gst-plugins-good,sebras/gst-plugins-good,StreamUtils/gst-plugins-good,hizukiayaka/gst-plugins-good,GStreamer/gst-plugins-good,kittee/gst-plugins-good,rawoul/gst-plugins-good,Kurento/gst-plugins-good,vatavuserban/gst-plugins-good,GrokImageCompression/gst-plugins-good,GrokImageCompression/gst-plugins-good,chamois94/gst-plugins-good,froggatt/gst-plugins-good-m,veo-labs/gst-plugins-good,ijsf/OpenWebRTC-gst-plugins-good,veo-labs/gst-plugins-good,shelsonjava/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,Kurento/gst-plugins-good,chamois94/gst-plugins-good,sh0/gst-plugins-good,pexip/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,stfl/gst-plugins-good,froggatt/gst-plugins-good-m,shelsonjava/gst-plugins-good,loshca/gst-plugins-good,sebras/gst-plugins-good,BigBrother-International/gst-plugins-good,Kurento/gst-plugins-good,hizukiayaka/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,shelsonjava/gst-plugins-good,ikonst/gst-plugins-good,GStreamer/gst-plugins-good,rawoul/gst-plugins-good,kittee/gst-plugins-good,BigBrother-International/gst-plugins-good,freedesktop-unofficial-mirror/gstreamer__gst-plugins-good,vatavuserban/gst-plugins-good,sebras/gst-plugins-good,stfl/gst-plugins-good