Use fetch() in a way that works for file URLs (#3071)

fetch returns a response code of 0 when it successfully loads a `file://` resource.

This means we can't just rely on `response.ok`.

Required for https://github.com/element-hq/element-call/issues/2994

src/initializer.tsx

@@ -28,6 +28,7 @@ import { getUrlParams } from "./UrlParams";
 import { Config } from "./config/Config";
 import { ElementCallOpenTelemetry } from "./otel/otel";
 import { platform } from "./Platform";
+import { isFailure } from "./utils/fetch";
 
 // This generates a map of locale names to their URL (based on import.meta.url), which looks like this:
 // {
@@ -79,7 +80,7 @@ const Backend = {
         },
       });
 
-      if (!response.ok) {
+      if (isFailure(response)) {
         throw Error(`Failed to fetch ${url}`);
       }