[wasm][gc] Finish current GC only once per isolate shutdown

R=clemensh@chromium.org

Also-By: clemensh@chromium.org
Bug: v8:9288, v8:8217
Change-Id: I1b4b7b5f06c49a6047d98a3a5db8bfa0c277be09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1627981
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61822}

src/wasm/wasm-engine.cc

@@ -586,9 +586,11 @@ void WasmEngine::RemoveIsolate(Isolate* isolate) {
       for (WasmCode* code : info->potentially_dead_code) {
         current_gc_info_->dead_code.erase(code);
       }
-      if (RemoveIsolateFromCurrentGC(isolate)) PotentiallyFinishCurrentGC();
     }
   }
+  if (current_gc_info_) {
+    if (RemoveIsolateFromCurrentGC(isolate)) PotentiallyFinishCurrentGC();
+  }
   if (auto* task = info->log_codes_task) task->Cancel();
   if (!info->code_to_log.empty()) {
     WasmCode::DecrementRefCount(VectorOf(info->code_to_log));