Loading spinner gets stuck if a WebView load fails

[jim-daf]

The three WebView clients in the app all show a loading spinner that is hidden from inside onPageFinished (directly or via the onLoaded callback). None of them override onReceivedError, so a main-frame load failure leaves the spinner spinning indefinitely.

The affected files:

• HTTPShortcuts/app/src/main/kotlin/ch/rmy/android/http_shortcuts/activities/documentation/DocumentationWebView.kt (calls showLoading() on start, hideLoading() only in onPageFinished)
• HTTPShortcuts/app/src/main/kotlin/ch/rmy/android/http_shortcuts/activities/response/ResponseWebView.kt (isLoading cleared via onLoaded only in onPageFinished)
• HTTPShortcuts/app/src/main/kotlin/ch/rmy/android/http_shortcuts/components/SinglePageBrowser.kt (same onLoaded pattern)

The documentation viewer is the most reachable case in practice, because it is configured with:

cacheMode = WebSettings.LOAD_CACHE_ELSE_NETWORK
blockNetworkLoads = true

So a cache miss for the bundled documentation (or any error reading the cached entry) cannot fall back to network. The user is stuck on the spinner with no way to know what happened.

Suggested fix: add onReceivedError(view, request, error) on each of the three WebViewClients and call hideLoading() / onLoaded() for request.isForMainFrame only. Sub-resource errors are still ignored so the spinner does not race off on transient asset failures. PR at #556.