RFR: 8303908: Add missing check in VTMS_transition_disable_for_all() for suspend mode

[Patricio Chilano Mateo]

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Please review this small fix. A suspender is a JvmtiVTMSTransitionDisabler monopolist, meaning VTMS_transition_disable_for_all() should not return while there is any active jvmtiVTMSTransitionDisabler. The code though is checking for active "all-disablers" but it's missing the check for active "single disablers".
I attached a simple reproducer to the bug which I used to test the patch. Not sure if it was worth adding a test so the patch contains just the fix.

Thanks,
Patricio

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Commit messages:
 - v1

Changes: https://git.openjdk.org/jdk/pull/12956/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12956&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303908
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12956.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12956/head:pull/12956

PR: https://git.openjdk.org/jdk/pull/12956