fix a compiler warning
fix a compiler warning

SuperSodaSea/itoa-benchmark,miloyip/itoa-benchmark,SuperSodaSea/itoa-benchmark,SuperSodaSea/itoa-benchmark,miloyip/itoa-benchmark,miloyip/itoa-benchmark,miloyip/itoa-benchmark,SuperSodaSea/itoa-benchmark,miloyip/itoa-benchmark,SuperSodaSea/itoa-benchmark