When a BOFT LoRA has no '{key}.alpha' entry, load_lora passes alpha=None.
BOFTAdapter.calculate_weight then hit 'if alpha > 0' with alpha=None,
raising a TypeError that the broad except in the caller swallowed, so the
weight was returned unchanged and the LoRA had no effect. Guard alpha the
same way OFTAdapter already does (None means no constraint).
