Fix a corner case of SparsePauliOp.apply_layout (backport #12375)

[mergify]

Summary

SparsePauliOp.apply_layout raises an error if a zero-qubit operator is given.
This PR fixes the case.

from qiskit.quantum_info import SparsePauliOp

op = SparsePauliOp("")
print(op.apply_layout(None, 3))

main branch

SparsePauliOp([''],
              coeffs=[1.+0.j])
Traceback (most recent call last):
  File "/Users/ima/tasks/4_2024/qiskit/terra/tmp/layout.py", line 5, in <module>
    print(op.apply_layout(None, 3))
  File "/Users/ima/tasks/4_2024/qiskit/terra/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py", line 1167, in apply_layout
    return new_op.compose(self, qargs=layout)
  File "/Users/ima/tasks/4_2024/qiskit/terra/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py", line 349, in compose
    q = np.logical_and(z1[:, np.newaxis], x2).reshape((-1, num_qubits))
ValueError: cannot reshape array of size 0 into shape (0)

this PR

SparsePauliOp(['III'],
              coeffs=[1.+0.j])

Although Pauli.apply_layout works correctly, I added the zero-qubit test cases to ensure it.

Details and comments

---

This is an automatic backport of pull request #12375 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 9083279815

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.001%) to 89.639%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	2	88.2%
crates/qasm2/src/lex.rs	4	93.38%

Totals
Change from base Build 9082210021:	-0.001%
Covered Lines:	62265
Relevant Lines:	69462

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💛 - Coveralls