Make the preview option stable against occasional invalid URL errors

[yhatt]

When opening multiple previews with --preview option, the preview window detector will sometimes fail with the parse error of empty URL for other type page.

node:internal/url:818
      href = bindingUrl.parse(input, base, true);
                        ^

TypeError: Invalid URL
    at new URL (node:internal/url:818:25)
    at idMatcher (/Users/yhatt/Programs/marp/marp-cli/lib/marp-cli-DSmb16j_.js:25490:33)
    at /Users/yhatt/Programs/marp/marp-cli/node_modules/puppeteer-core/lib/cjs/third_party/mitt/mitt.js:62:7
    at Array.map (<anonymous>)
    at Object.emit (/Users/yhatt/Programs/marp/marp-cli/node_modules/puppeteer-core/lib/cjs/third_party/mitt/mitt.js:61:20)
    at CdpBrowser.emit (/Users/yhatt/Programs/marp/marp-cli/node_modules/puppeteer-core/lib/cjs/puppeteer/common/EventEmitter.js:83:23)
    at #onAttachedToTarget (/Users/yhatt/Programs/marp/marp-cli/node_modules/puppeteer-core/lib/cjs/puppeteer/cdp/Browser.js:158:18)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5) {
  code: 'ERR_INVALID_URL',
  input: ''
}

This PR fixes that to narrow check only for the target that is having page type.