Fix unwrapped empty optional error for default ECH in FizzTool

Summary:
Fixes a bug where the default ECH cli argument in the client fizz tool attempts to
unwrap an empty optional.

Reviewed By: knekritz

Differential Revision: D55922129

fbshipit-source-id: 5209eb20be0a5cc98d293830264e7a800a97e63c

fizz/tool/FizzClientCommand.cpp

@@ -803,6 +803,7 @@ int fizzClientCommand(const std::vector<std::string>& args) {
 
   if (ech) {
     // Use default ECH config values.
+    echConfigList = ech::ECHConfigList{};
     auto echConfigContents = getDefaultECHConfigs();
     echConfigList->configs = std::move(echConfigContents);
   } else if (!echConfigsBase64.empty()) {