Don't treat dynamic data as a function (#19672)

Sometimes an integration test was throwing "TypeError: Cannot read properties of
null (reading 'call')" because a value was nil in the app-db, but the code was
treating it as if it was always a map and could be called as a function.

The original code wasn't respecting Clojure's nil punning good practices. In
Clojure, it's often recommended to not use dynamic data as functions, because if
they're nil, in CLJS we'll get an exception and as usual in CLJS, the stacktrace
won't be very readable.

We should prefer contains? or get, which will work just fine with nil values,
and only use data as a function if it's static, e.g. a map defined in a def.

src/status_im/contexts/wallet/events.cljs

@@ -148,7 +148,7 @@
    (let [tokens     (data-store/rpc->tokens raw-tokens-data)
          add-tokens (fn [stored-accounts tokens-per-account]
                       (reduce-kv (fn [accounts address tokens-data]
-                                   (if (accounts address)
+                                   (if (contains? accounts address)
                                      (update accounts address assoc :tokens tokens-data)
                                      accounts))
                                  stored-accounts