index/confirm tasks: these tasks no longer need to open the decoder to perform said tasks

app/task/conform/conform.cpp

@@ -42,9 +42,7 @@ void ConformTask::Action()
 
     connect(decoder.get(), &Decoder::IndexProgress, this, &ConformTask::ProgressChanged);
 
-    decoder->Open();
     decoder->Conform(params_, &IsCancelled());
-    decoder->Close();
 
     emit Succeeded();
   }

app/task/index/index.cpp

@@ -42,9 +42,7 @@ void IndexTask::Action()
 
     connect(decoder.get(), &Decoder::IndexProgress, this, &IndexTask::ProgressChanged);
 
-    decoder->Open();
     decoder->Index(&IsCancelled());
-    decoder->Close();
 
     emit Succeeded();
   }