fix(nsis): properly handle Webview2 download return value

[0rvar]

The NSIS template was changed in #9605 to use NSISdl instead of nsis_tauri_utils for downloading Webview2, but the return value handling was not adjusted from comparing against 0, to the return value of NSISdl::download:

The return value is pushed to the stack:

  "cancel" if cancelled
  "success" if success
  otherwise, an error string describing the error

The issue can be reliably reproduced with Windows Sandbox, which never has Webiew2 preinstalled.

This PR adjusts the NSIS template to properly check the return value.

Before	After - success	After - offline

[github-actions]

Package Changes Through 8e60414

There are 2 changes which include tauri-bundler with patch, tauri with patch

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
tauri-bundler	1.7.0	1.7.1
tauri	1.8.0	1.8.1
@tauri-apps/cli	1.6.2	1.6.3
tauri-cli	1.6.2	1.6.3

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