getHaveServerData: Fix unsafe zulipVersion access causing crash on login

This fixes a regression introduced in 3b811d6 that made it
impossible to log into a new account, by crashing just after
completing authentication with the message "zulipVersion must be
non-null".

Oops: getHaveServerData was not an OK place to call
getServerVersion. From the jsdoc:

 * This function assumes we have server data for this account, and if not it
 * may throw.  […]

So, abandon that selector and access zulipVersion safely.

While I was at it, I double-checked `Account['zulipVersion']` and
`Account['zulipFeatureLevel']` …and found that their jsdocs weren't
right about when those fields were null. Fix that, copying some text
from the jsdoc of `Account['userId']`.

Author: chrisbobbe

src/haveServerDataSelectors.js

@@ -2,11 +2,7 @@
 
 import type { GlobalState, PerAccountState } from './types';
 import { getUsers } from './directSelectors';
-import {
-  tryGetAuth,
-  tryGetActiveAccountState,
-  getServerVersion,
-} from './account/accountsSelectors';
+import { tryGetAuth, tryGetActiveAccountState, getAccount } from './account/accountsSelectors';
 import { getUsersById } from './users/userSelectors';
 import { kMinAllowedServerVersion } from './api/apiErrors';
 
@@ -119,9 +115,16 @@ export const getHaveServerData = (state: PerAccountState): boolean => {
     return false;
   }
 
+  const { zulipVersion } = getAccount(state);
+
+  // The server version comes with the rest of the server data.
+  if (!zulipVersion) {
+    return false;
+  }
+
   // We may have server data, but it would be from an ancient server that we
   // don't support, so it might be malformed.
-  if (!getServerVersion(state).isAtLeast(kMinAllowedServerVersion)) {
+  if (!zulipVersion.isAtLeast(kMinAllowedServerVersion)) {
     return false;
   }
 

src/types.js

@@ -86,9 +86,11 @@ export type Account = {|
    * Because a server deploy invalidates event queues, this means the value
    * is always up to date for a server we have an active event queue on.
    *
-   * This is `null` just when representing an account which was last used on
-   * a version of the app which didn't record this information.  It's never
-   * `null` for an account for which we have server data.
+   * This is `null` briefly when we've logged in but not yet completed our
+   * first initial fetch on the account.  It's also `null` when representing
+   * an account which was last used on a version of the app which didn't
+   * record this information.  It's never `null` for an account for which we
+   * have server data.
    *
    * For use in:
    *  * how we make some API requests, in order to keep the logic isolated
@@ -107,9 +109,11 @@ export type Account = {|
    * This is designed to provide a simple way for mobile apps to decide
    * whether the server supports a given feature or API change.
    *
-   * This is `null` just when representing an account which was last used on
-   * a version of the app which didn't record this information.  It's never
-   * `null` for an account for which we have server data.
+   * This is `null` briefly when we've logged in but not yet completed our
+   * first initial fetch on the account.  It's also `null` when representing
+   * an account which was last used on a version of the app which didn't
+   * record this information.  It's never `null` for an account for which we
+   * have server data.
    *
    * Like zulipVersion, we learn the feature level from /server_settings
    * at the start of the login process, and again from /register when