Fix nested parking of threads while setting up a garbage collection.

Source/platform/heap/Heap.cpp

Index: Source/platform/heap/Heap.cpp
diff --git a/Source/platform/heap/Heap.cpp b/Source/platform/heap/Heap.cpp
index d1f421585fb0f096e10c0b5788c4f529fdfcdc4b..430e1121cd22fee3d4651aea19f3667277737c7f 100644
--- a/Source/platform/heap/Heap.cpp
+++ b/Source/platform/heap/Heap.cpp
@@ -1882,7 +1882,8 @@ void Heap::collectGarbage(ThreadState::StackState stackState, ThreadState::GCTyp
     // the GC.
     if (!gcScope.allThreadsParked()) {
         // Restore the original GCState.
-        state->setGCState(originalGCState);
+        if (LIKELY(state->gcState() == ThreadState::StoppingOtherThreads))
+            state->setGCState(originalGCState);
         return;
     }