RFR: 8261299: Use-after-free on failure path in LinuxPackage.c, getJvmLauncherLibPath

[Aleksey Shipilev]

SonarCloud instance reports a new warning after JDK-8254702:
 "Use of memory after it is freed"

char* getJvmLauncherLibPath(void) {
       ...
        popenStatus = popenCommand(pkgQueryCmd, pkg->name, findLauncherLib,
                                                        &launcherLibPath);
        if (popenStatus) {
            free(launcherLibPath); <---- frees here
            goto cleanup;
        }
    }

cleanup:
    free(modulePath);
    freePackageDesc(pkg);

    return launcherLibPath; <--- here
}

We need to null it out before returning.

Additional testing:
 - [x] Linux x86_64 (Ubuntu) `tools/jpackage`

-------------

Commit messages:
 - Null it out

Changes: https://git.openjdk.java.net/jdk/pull/2453/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2453&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261299
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2453.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2453/head:pull/2453

PR: https://git.openjdk.java.net/jdk/pull/2453