initial fetch: Merge `fetchInitialData` and `doInitialFetch`.
initial fetch: Merge `fetchInitialData` and `doInitialFetch`.

At this point `fetchInitialData` does not only "fetch data" but also
does `sendOutbox`.

Merging this into `doInitialFetch` allows us to skip the whole
initialization phase in case of a 4xx error in the `register` call.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile