fix: assert overwrite wallet first

[XuNeal]

Summary of Changes

• assert the target wallet before search existed wallet

https://imtoken.atlassian.net/browse/R2D2-11396

Motivation and Context

How Has This Been Tested? (Test Plan)

Other information

Screenshots (if appropriate):

Final checklist

• Did you test both iOS and Android(if applicable)?
• Is a security review needed(consenlabs/security)?

Security checklist (only for leader check)

• No backdoor risk
  • Check for unknown network request urls, and script/shell files with unclear purposes,
  • The backend service cannot expose leaked data interfaces for various reasons (even for testing purposes)
• No network communication protocol risk
  • Check whether to introduce unsafe network calls such as http/ws
• No import potentially risk 3rd library
  • Check whether 3rd dependent library is import
  • Don't use an unknown third-party library
  • Check the 3rd library sources are fetched from normal sources, such as npm, gomodule, maven, cocoapod, Do not use unknown sources
  • Check github Dependabot alerts, Whether to add new issues
• Private data not exposed
  • Check whether there are exclusive ApiKey, privatekey and other private information uploaded to git
  • Check if the packaged keystore has been uploaded to git