util: avoid out-of-bounds arguments index access

This updates util.inspect() to avoid accessing out-of-range indices of the arguments object, which is known to cause optimization bailout.

Based on an average of 10 runs of the benchmark in benchmark/util/inspect.js, this change improves the performance of util.inspect by about 10%.

Relates to https://github.com/nodejs/node/issues/10323

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

util