Auto merge of #83028 - GuillaumeGomez:prevent-js-error-if-no-filter, …

…r=Nemo157

Prevent JS error when there is no dependency or other crate documented (or --disable-per-crate-search has been used)

When there is only one crate, the dropdown is removed, creating an error (that you can see pretty easily on docs.rs for example).

r? `@jyn514`

src/librustdoc/html/static/main.js

@@ -2948,7 +2948,11 @@ function defocusSearchBar() {
         search_input.removeAttribute('disabled');
 
         var crateSearchDropDown = document.getElementById("crate-search");
-        crateSearchDropDown.addEventListener("focus", loadSearch);
+        // `crateSearchDropDown` can be null in case there is only crate because in that case, the
+        // crate filter dropdown is removed.
+        if (crateSearchDropDown) {
+            crateSearchDropDown.addEventListener("focus", loadSearch);
+        }
         var params = getQueryStringParams();
         if (params.search !== undefined) {
             loadSearch();