mono_runtime_class_init_full: handle spurious wakeups

the condition variable may be signaled even if the initialization by
the other thread is not done yet.  Handle spurious wakeups the same
way as timeouts: go around once more from the beginning.

Fixes dotnet#96872

src/mono/mono/metadata/object.c

@@ -614,8 +614,8 @@ mono_runtime_class_init_full (MonoVTable *vtable, MonoError *error)
 		if (!lock->done) {
 			int timeout_ms = 500;
 			int wait_result = mono_coop_cond_timedwait (&lock->cond, &lock->mutex, timeout_ms);
-			if (wait_result == -1) {
-				/* timed out - go around again from the beginning.  If we got here
+			if (wait_result == -1 || (wait_result == 0 && !lock->done)) {
+				/* timed out or spurious wakeup - go around again from the beginning.  If we got here
 				 * from the "is_blocked = FALSE" case, above (another thread was
 				 * blocked on the current thread, but on a lock that was already
 				 * done but it didn't get to wake up yet), then it might still be
@@ -646,7 +646,7 @@ mono_runtime_class_init_full (MonoVTable *vtable, MonoError *error)
 					g_hash_table_remove (type_initialization_hash, vtable);
 				mono_type_initialization_unlock ();
 				goto retry_top;
-			} else if (wait_result == 0) {
+			} else if (wait_result == 0 && lock->done) {
 				/* Success: we were signaled that the other thread is done.  Proceed */
 			} else {
 				g_assert_not_reached ();