gst1: Fix querying of duration of MP3s
gst1: Fix querying of duration of MP3s

adamcik/mopidy,mokieyue/mopidy,mokieyue/mopidy,mopidy/mopidy,ZenithDK/mopidy,mopidy/mopidy,vrs01/mopidy,ZenithDK/mopidy,vrs01/mopidy,tkem/mopidy,adamcik/mopidy,jodal/mopidy,kingosticks/mopidy,ZenithDK/mopidy,adamcik/mopidy,mokieyue/mopidy,mopidy/mopidy,vrs01/mopidy,jcass77/mopidy,tkem/mopidy,mokieyue/mopidy,vrs01/mopidy,ZenithDK/mopidy,kingosticks/mopidy,tkem/mopidy,jodal/mopidy,jcass77/mopidy,kingosticks/mopidy,tkem/mopidy,jodal/mopidy,jcass77/mopidy