Check for metadata before getting a value for the sampler.
Check for metadata before getting a value for the sampler.

Followup to r1835351. The eager evaluating led to test failures.
It would probably better to store a zero as Integer and Long instead of
calling Long#valueOf(0L) each time we need a zero.

Bugzilla Id: 62426


git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1835661 13f79535-47bb-0310-9956-ffa450edef68

Former-commit-id: db56b7d07d98b277d3070289fcd6f260d1dbf6d6
apache/jmeter,apache/jmeter,ham1/jmeter,etnetera/jmeter,benbenw/jmeter,apache/jmeter,apache/jmeter,etnetera/jmeter,ham1/jmeter,benbenw/jmeter,etnetera/jmeter,apache/jmeter,benbenw/jmeter,ham1/jmeter,ham1/jmeter,etnetera/jmeter,etnetera/jmeter,benbenw/jmeter,ham1/jmeter