Use StandardCharset instead of looking one up by string.
Use StandardCharset instead of looking one up by string.

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1780464 13f79535-47bb-0310-9956-ffa450edef68

Former-commit-id: 19bbd30f4e9f3a5d4faed1def588328c211497ad
etnetera/jmeter,ham1/jmeter,apache/jmeter,apache/jmeter,benbenw/jmeter,benbenw/jmeter,etnetera/jmeter,etnetera/jmeter,ham1/jmeter,etnetera/jmeter,benbenw/jmeter,ham1/jmeter,etnetera/jmeter,ham1/jmeter,apache/jmeter,ham1/jmeter,apache/jmeter,benbenw/jmeter,apache/jmeter