inspector: fix crash when receiving non json message

Author: islandryu

src/inspector_io.cc

@@ -353,6 +353,9 @@ std::optional<std::string> InspectorIoDelegate::GetTargetSessionId(
   std::string_view view(message.data(), message.size());
   std::unique_ptr<protocol::DictionaryValue> value =
       protocol::DictionaryValue::cast(JsonUtil::parseJSON(view));
+  if (!value) {
+    return std::nullopt;
+  }
   protocol::String target_session_id;
   protocol::Value* target_session_id_value = value->get("sessionId");
   if (target_session_id_value) {