Handle prefilled input value

[ob-ivan]

Consider following scenario with instant-submit option enabled:

1. User inputs a search query and the page reloads to show search results.
2. On the loaded page the search field is prefilled with the current search query.
3. User clicks mic button to enter a new query.
4. Case 1: Chrome blocks device access.
   • Expected behavior: nothing happens.
   • Actual behavior: the auto-submit feature submits the form, and the page is reloaded.
5. Case 2: mic access is granted successfully.
   • Expected behavior: the input is cleared before the recognition starts.
   • Actual behavior: the new (recognized) query is appended to the previous one, and the search starts with the concatenation, providing incoherent results.