Fix use-after-free in proxy resolver

Bug: 139806216
Test: m -j proxy_resolver_v8_unittest && adb sync && adb shell \
      /data/nativetest64/proxy_resolver_v8_unittest/proxy_resolver_v8_unittest

Change-Id: I663829a8a7467f50f9b11fd8b787108ff5d64acc
(cherry picked from commit 061a73bd2d79c4bec5780b9b84dceead30a2b767)