Prevent tab title to "null" if the URL is a search one

[GuillaumeGomez]

When we arrive on page with a search parameter in the URL, until the results are displayed, the page title is "null". It's because of this code:

if (params.search !== undefined) {
    var search = searchState.outputElement();
    search.innerHTML = "<h3 style=\"text-align: center;\">" +
       searchState.loadingText + "</h3>";
    searchState.showResults(search);
    loadSearch();
}

In searchState.showResults, we have this:

document.title = searchState.title;

But since it's null, we set it as title. This PR fixes it.

r? @jsha

[rust-highfive]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez

[jsha]

@bors r+

[bors]

📌 Commit 222126a has been approved by jsha

[GuillaumeGomez]

@bors: rollup