Defend the case that WasmHandleBase::wasm() is null for canary function

Signed-off-by: Ingwon Song <igsong@google.com>

Author: ingwonsong

src/wasm.cc

@@ -449,6 +449,9 @@ void WasmBase::finishShutdown() {
 
 bool WasmHandleBase::canary(const std::shared_ptr<PluginBase> &plugin,
                             const WasmHandleCloneFactory &clone_factory) {
+  if (this->wasm() == nullptr) {
+    return false;
+  }
   auto configuration_canary_handle = clone_factory(shared_from_this());
   if (!configuration_canary_handle) {
     this->wasm()->fail(FailState::UnableToCloneVm, "Failed to clone Base Wasm");