Fix return_dict_in_generate bug in InstructBlip generate function (#25246)
Fix bug in InstructBlip generate function
Previously, the postprocessing conducted on generated sequences in InstructBlip's generate function assumed these sequences were tensors (i.e. that `return_dict_in_generate == False`).
This commit checks whether the result of the call to the wrapped language model `generate()` is a tensor, and if not attempts to postprocess the sequence attribute of the returned results object.