Update decoding.py (openai#1155)

* Update decoding.py

Following the suggestions of @Jeronymous in openai#914 and openai#924, it solves the problem of endless loop.

* Removed blank line and whitespaces in empty lines.

* Suggested changes according to the linter

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Co-authored-by: Jong Wook Kim <jongwook@openai.com>

whisper/decoding.py

@@ -471,6 +471,13 @@ def apply(self, logits: Tensor, tokens: Tensor):
                 # timestamps shouldn't decrease; forbid timestamp tokens smaller than the last
                 logits[k, self.tokenizer.timestamp_begin : timestamps[-1]] = -np.inf
 
+                # to force that timestamps are strictly increasing
+                if last_was_timestamp and not penultimate_was_timestamp:
+                    timestamp_last = timestamps[-1]
+                else:
+                    timestamp_last = timestamps[-1] + 1
+                logits[k, self.tokenizer.timestamp_begin : timestamp_last] = -np.inf
+
         if tokens.shape[1] == self.sample_begin:
             # suppress generating non-timestamp tokens at the beginning
             logits[:, : self.tokenizer.timestamp_begin] = -np.inf