RFR: backporting fix for 7903547: libffmpeg sample crashes JVM

Tue Sep 26 10:55:59 UTC 2023

backporting fix for 7903547: libffmpeg sample crashes JVM from 'panama' branch

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Commit messages:
 - backporting fix for 7903547: libffmpeg sample crashes JVM

Changes: https://git.openjdk.org/jextract/pull/129/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=129&range=00
  Stats: 241 lines in 1 file changed: 63 ins; 79 del; 99 mod
  Patch: https://git.openjdk.org/jextract/pull/129.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/129/head:pull/129

PR: https://git.openjdk.org/jextract/pull/129