registerAbort: Don't infinite-retry if reason is 'unexpected'

I'm not aware of any actual cases of this happening. But with a
totally unexpected error, we don't really have reason to hope that
infinite-retrying will help a /register succeed, so we should abort
and let the user know.

src/message/fetchActions.js

@@ -224,7 +224,7 @@ export const registerAbort = (reason: RegisterAbortReason): ThunkAction<Promise<
   getState,
 ) => {
   dispatch(registerAbortPlain(reason));
-  if (getHaveServerData(getState())) {
+  if (getHaveServerData(getState()) && reason !== 'unexpected') {
     // Try again, forever if necessary; the user has an interactable UI and
     // can look at stale data while waiting.
     //