RFR: 8301760: Fix possible leak in SpNegoContext dispose

[Yuri Nesterenko]

On Fri, 3 Feb 2023 14:12:42 GMT, Yuri Nesterenko <yan at openjdk.org> wrote:

> This small change should fix a possible under certain circumstances native memory leak. In fact, the actual leak was reported in production.

Pre-submit windows64 "hs/tier1 compiler" test timeout  failure is apparently unrelated (detected in other PRs submitted around the same time)

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PR: https://git.openjdk.org/jdk/pull/12407