create_weights_overlap_linear computed the right-edge ramp with
weights_torch[-context_overlap:], which becomes weights_torch[0:]
(the whole tensor) when context_overlap is 0, while the ramp is a
zero-length tensor. Assigning the empty ramp raised a RuntimeError.
context_overlap == 0 is reachable: the context-window nodes allow a
minimum of 0, and the WAN/LTXV nodes derive it via max(overlap // 4, 0).
Return the all-ones weights early when there is no overlap band to blend.
