Check number of qubits in PauliOp.eval (Qiskit/qiskit-aqua#1105)
Check number of qubits in PauliOp.eval (Qiskit/qiskit-aqua#1105)

Without this check, a nonsense answer may be returned silently for
invalid input. For example, applying a Pauli Y operator to two qubits,
Y.eval('11') flips both qubits, but returns the wrong coefficient.
This behavior seems to be an unintended accident.

Co-authored-by: Steve Wood <df319c8b10182f101be29ecf0d4d148dec6c4bfc@users.noreply.github.com>
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py