doInitialFetch [nfc]: Put initData declaration just before initialization

As Greg points out [1]:

> Logically I'd like to think of it as a `const`, where the
> declaration and initializer are inseparable.

[1] #5282 (comment)

Author: chrisbobbe

src/message/fetchActions.js

@@ -451,10 +451,9 @@ export const doInitialFetch = (): ThunkAction<Promise<void>> => async (dispatch,
   dispatch(registerStart());
   const auth = getAuth(getState());
 
-  let initData: InitialData;
-
   const haveServerData = getHaveServerData(getState());
 
+  let initData: InitialData;
   try {
     initData = await tryFetch(
       // Currently, no input we're giving `registerForEvents` is