Use parameters + buffers when deciding upscale_dtype

[universome]

Sometimes, the decoder might lack parameters and only buffers (e.g., this happens when we manually need to convert all the parameters to buffers — e.g. to avoid packing fp16 and fp32 parameters with FSDP)

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Fixes # (issue)

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[sayakpaul]

Could you maybe elaborate a bit more where this is useful?