fix(browser): prevent registration-induced crash (#6799)

Fixed a bug where `authenticatorSelection` may be undefined and cause
the extension to crash when attempting to register a new credential.

Co-authored-by: SmithThe4th <gsmith@bitwarden.com>

apps/browser/src/vault/fido2/content/page-script.ts

@@ -62,9 +62,9 @@ navigator.credentials.create = async (
   }
 
   const fallbackSupported =
-    (options?.publicKey?.authenticatorSelection.authenticatorAttachment === "platform" &&
+    (options?.publicKey?.authenticatorSelection?.authenticatorAttachment === "platform" &&
       browserNativeWebauthnPlatformAuthenticatorSupport) ||
-    (options?.publicKey?.authenticatorSelection.authenticatorAttachment !== "platform" &&
+    (options?.publicKey?.authenticatorSelection?.authenticatorAttachment !== "platform" &&
       browserNativeWebauthnSupport);
   try {
     const response = await messenger.request(