RFR: 8207025: Simplify PathString::set_value() in arguments.cpp [v2]

[Ioi Lam]

> Please review this trivial change. Remove unnecessary NULL check and change return type to void, since the function will never return with a failure status.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  @dholmes-ora comments: changed implementation to work with JvmtiEnv::SetSystemProperty

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7981/files
  - new: https://git.openjdk.java.net/jdk/pull/7981/files/6a3fc77b..0397499f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7981&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7981&range=00-01

  Stats: 41 lines in 3 files changed: 27 ins; 1 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7981.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7981/head:pull/7981

PR: https://git.openjdk.java.net/jdk/pull/7981