RFR: 8276915: Crash on iOS 15.1 in GlassRunnable::dealloc

[Jose Pereda]

After https://bugs.openjdk.java.net/browse/JDK-8275723 and the fix applied to `GlassApplication.m` for macOS, this PR is a follow-up and applies the same fix to `GlassApplication.m` on iOS to prevent the crash.

I've only tested on iOS 15.0 building from macOS 11.6, but it should fix the crash when building from macOS 12.

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Commit messages:
 - Avoid crash on iOS

Changes: https://git.openjdk.java.net/jfx/pull/665/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=665&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276915
  Stats: 18 lines in 1 file changed: 4 ins; 13 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/665.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/665/head:pull/665

PR: https://git.openjdk.java.net/jfx/pull/665