30: Fix regression introduced in solution for Rust track exercise "Nth Prime".

Created by  Aaw9nJhsNmfzFih9mKyNw9mV8CgERXJkRa1kK1Kx3LQH  on September 2, 2021
ZSKHCSQ5VEHFCQPJMX6EH6BSRSDU4DPAW3QRR3JZKZMYLOO72X7QC
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