webview: Fix (new) bug where message fetch never works.
webview: Fix (new) bug where message fetch never works.

Before this fix, our longstanding bug where messages don't load on
entering a narrow was reproducing for me every time in a test
environment.  Very handy for debugging!

Unfortunately, this particular issue seems to have been introduced
just today, in 8376ec0a9 "refactor: Split webViewHandleUpdates".
So the longstanding bug probably remains after this fix.

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