8212207: runtime/InternalApi/ThreadCpuTimesDeadlock.java crashes with SEGV in pthread_getcpuclockid+0x0

Skip non-JavaThreads that have not reached a minimal initialization point - setting their stack size

Reviewed-by: kbarrett, stuefe

src/hotspot/share/services/management.cpp

@@ -1645,6 +1645,12 @@ void ThreadTimesClosure::do_thread(Thread* thread) {
     return;
   }
 
+  // NonJavaThread instances may not be fully initialized yet, so we need to
+  // skip any that aren't - check for zero stack_size()
+  if (!thread->is_Java_thread() && thread->stack_size() == 0) {
+    return;
+  }
+
   if (_count >= _names_len || _count >= _times_len) {
     // skip if the result array is not big enough
     return;