Add Language Model Decoder

Closes #142 (closed)

Taking over from !222 (closed)

dan/ocr/predict/prediction.py

@@ -93,7 +93,7 @@ class DAN:
         self.decoder = decoder
         self.lm_decoder = None
 
-        if use_language_model:
+        if use_language_model and parameters["lm_decoder"]["language_model_weight"] > 0:
             self.lm_decoder = CTCLanguageDecoder(
                 language_model_path=parameters["lm_decoder"]["language_model_path"],
                 lexicon_path=parameters["lm_decoder"]["lexicon_path"],
@@ -509,6 +509,9 @@ def run(
         model, parameters, charset, mode="eval", use_language_model=use_language_model
     )
 
+    # Do not use LM with invalid LM weight
+    use_language_model = dan_model.lm_decoder is not None
+
     images = image_dir.rglob(f"*{image_extension}") if not image else [image]
     for image_batch in list_to_batches(images, n=batch_size):
         process_batch(