[Issue 11594] synchronized causing segfault instead of Error.

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=11594

--- Comment #6 from github-bugzilla at puremagic.com ---
Commit pushed to stable at https://github.com/dlang/druntime

https://github.com/dlang/druntime/commit/a2ead6dd04efdfeb283b72daf167e85fe8db9c49
Fix issue 11594: Check if the monitor is null in _d_monitorenter

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