web: Add an extra check for if the WASM download failed

[danielhjacobs]

No description provided.

[torokati44]

For context, the full message text might be something like this:
"WebAssembly compilation aborted: Network error: Failed to read from a ReadableStream."

(According to your message on Discord.)

[danielhjacobs]

Yup:

https://github.com/ruffle-rs/ruffle/issues?q=is%3Aissue+is%3Aopen+%22WebAssembly+compilation+aborted%3A+Network+error%3A+Failed+to+read+from+a+ReadableStream%22+

I assume this has been a possible error since #7396, but it may be newer, as the first report about it was Nov 9, 2023 (with a build from September 1)

[danielhjacobs]

Also of note is that this is likely the most common error being suppressed by the problem fixed by #17976, which is why it hasn't come up in any reports of recent builds.