Zero-length dynamic control vectors are misinterpreted as scalar controls

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Describe the bug

CUDA-Q fails when a dynamically sized control vector is empty. An empty control set should apply the operation without controls, but the runtime instead treats the vector pointer as a scalar qubit pointer.

Steps to reproduce the bug

import cudaq

@cudaq.kernel
def flip_on_slice(v: cudaq.qview, n: int):
    x.ctrl(v[1:n + 1], v[0])

@cudaq.kernel
def controlled(n: int):
    q = cudaq.qvector(n + 1)
    flip_on_slice(q, n)
    mz(q)

print(cudaq.sample(controlled, 0, shots_count=20))

Expected behavior

v[1:1] is an empty control set, so x applies normally to v[0]: { 1:20 }

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• CUDA-Q version: main
• Python version: N/A
• C++ compiler: N/A
• Operating system: N/A

Suggestions

No response