storage: Account explicitly for first startup, too.

Based on Robert Hönig's observation of what happens on first startup
of the app.

src/actionTypes.js

@@ -92,9 +92,10 @@ import type {
 
 export type RehydrateAction = {
   type: typeof REHYDRATE,
-  // The payload will have `null` at each key where an error was encountered
-  // in reading the persisted store.
-  payload: GlobalState | { accounts: null },
+  // The payload will be empty on first startup or if the persisted store is
+  // just missing keys, and will have `null` at each key where an error was
+  // encountered in reading the persisted store.
+  payload: GlobalState | { accounts: null } | {},
   error: ?Object,
 };
 

src/nav/navReducers.js

@@ -1,5 +1,6 @@
 /* @flow */
 import type {
+  GlobalState,
   NavigationState,
   NavAction,
   RehydrateAction,
@@ -22,12 +23,12 @@ import {
 const initialState = getStateForRoute('loading') || NULL_NAV_STATE;
 
 const rehydrate = (state: NavigationState, action: RehydrateAction): NavigationState => {
-  // If there's an error reading the persisted state, we'll get a
-  // RehydrateAction with `null` at each key.
-  if (action.payload.accounts === null) {
+  if (!action.payload || !action.payload.accounts) {
     return getStateForRoute('welcome') || state;
   }
-  return getInitialNavState(action.payload) || state;
+  // $FlowFixMe: Flow oddly doesn't see the refinement from the condition above.
+  const rehydratedState = (action.payload: GlobalState);
+  return getInitialNavState(rehydratedState) || state;
 };
 
 const accountSwitch = (state: NavigationState, action: AccountSwitchAction): NavigationState =>

src/session/sessionReducers.js

@@ -69,14 +69,18 @@ const loginSuccess = (state: SessionState, action: LoginSuccessAction): SessionS
   needsInitialFetch: true,
 });
 
-const rehydrate = (state: SessionState, action: RehydrateAction): SessionState => ({
-  ...state,
-  isHydrated: true,
-  // On rehydration, do an initial fetch if we have access to an account
-  // (indicated by the presence of an api key). Otherwise, the initial fetch
-  // will be initiated on loginSuccess.
-  needsInitialFetch: !!(action.payload.accounts && getAuth(action.payload).apiKey),
-});
+const rehydrate = (state: SessionState, action: RehydrateAction): SessionState => {
+  const payload = { action };
+  const haveApiKey = !!(payload && payload.accounts && getAuth(payload).apiKey);
+  return {
+    ...state,
+    isHydrated: true,
+    // On rehydration, do an initial fetch if we have access to an account
+    // (indicated by the presence of an api key). Otherwise, the initial fetch
+    // will be initiated on loginSuccess.
+    needsInitialFetch: haveApiKey,
+  };
+};
 
 const realmInit = (state: SessionState, action: RealmInitAction): SessionState => ({
   ...state,