Fail the upload when the converter returns no document

[andiwand]

What

doOnlineConvert read the Location header without checking it was there:

val redirectUrl = connection.getHeaderField("Location")
return Uri.parse(basePath + redirectUrl)

use.opendocument.app answers a converted document with a redirect to it, so when it refuses a file there is no Location, getHeaderField returns null, and the null goes straight into the concatenation. The loader then reported success for the uri https://use.opendocument.appnull/.

How it shows up

Opening a truncated .odt on an emulator:

D/ODR      CORE failed
E/ODR      app.opendocument.core.OdrException: not a zip file
I/smn      loader_error_CORE
...user accepts the "upload this file?" offer...
I/smn      loader_success_ONLINE content_type content
E/ODR      java.lang.RuntimeException: loading https://use.opendocument.appnull/ failed:
           -2 net::ERR_NAME_NOT_RESOLVED

Two things go wrong: the user gets a WebView DNS error page rather than the "could not open" dialog and the offer to reopen, and the log line blames DNS instead of the server refusing the document.

The fix

Treat a missing Location the way doTransferUpload already treats an empty body — throw an IOException carrying the response code and the error body, so loadSync routes it through callOnError.

The guard is on the header rather than on the status code alone, so a 2xx-with-Location response keeps working; the code is included for diagnostics.

Notes

The file that surfaced this is genuinely corrupt — it carries two end-of-central-directory records, and the authoritative last one points at offset 24822, which is zeros, while the real central directory sits at 24089. unzip rejects it too, so the core's not a zip file is correct and unchanged here. This PR is only about the fallback path lying about having succeeded.

The bug predates the Kotlin conversion; the pre-conversion Java had the identical two lines.

Not covered by a unit test: doOnlineConvert is private, needs a live HttpURLConnection, and Uri.parse needs a real Android runtime — the existing OnlineLoaderTest only exercises the pure isSupported/isConvertible predicates, and there is no MockWebServer/Robolectric setup to hang a test on.

Test plan

• ./gradlew spotlessCheck testProDebugUnitTest — green