Don't attempt to fix errors in the music file when there is no music file.

windows_archive/archiveloop

@@ -188,9 +188,12 @@ function mount_and_fix_errors_in_cam_file () {
 }
 
 function mount_and_fix_errors_in_music_file () {
+  if [ -e "$MUSIC_MOUNT" ]
+  then
     ensure_music_file_is_mounted
     fix_errors_in_music_file
     unmount_music_file
+  fi
 }
 
 function mount_and_fix_errors_in_files () {