Search form doesn't remember current search category

[bmispelon]

When searching for a term and using a more specific category than "All", the search form doesn't remember which category is being used.

Steps to reproduce:

1. Search for "localize"
2. Choose "API reference"
3. In the search input at the top, type "unlocalize" instead of "localize"

Expectation:

The search results for "unlocalize" in the category "API reference" should be displayed

Actual behavior

The search results for "unlocalize" in the "All" category are displayed instead.