Fix outdated search results

[DeD1rk]

This fixes a problem where incorrect search results may appear. When an api call was triggered, its result was used even if during the asynchronous gap, something changes such that the result should no longer be used. For example:

• When searching for 'a', a timer is started.
• After 300ms, an http request is sent.
• Before the corresponding response is received, the user removes the query, so the state should remain loading.
• The response arrives, and handling of the old 'a' search continues, emitting a new incorrect state.

This PR eliminates the problem by discarding a response if the search query has changed. Note that exceptions thrown in the api call will still result in an exception state being emitted.