Fix SSE not working with streamable HTTPS

Author: leehack

.vscode/launch.json

@@ -4,6 +4,13 @@
   // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
   "version": "0.2.0",
   "configurations": [
+    {
+      "name": "server_simple_streamable_https",
+      "type": "dart",
+      "request": "launch",
+      "program": "example/server_simple_streamable_https.dart",
+      "console": "terminal"
+    },
     {
       "name": "client_streamable_https",
       "type": "dart",