[FIX] web_responsive: Skip re-search when not writing

When the user uses TAB or SHIFT+TAB to navigate in search results, he can trigger a SHIFT-only keydown event without noticing, which would reset the selected result position to the first or last.

It is disturbing, so, to avoid that problem, the re-search is only triggered if the currently pressed key has length=1 or is Backspace, which will skip most keys that are not actually writing a character into the search input, like i.e. "Shift", "Alt", "F4", etc.

In addition to that, to detect if the search results is empty, the `:empty` selector is not trustable because it considers not empty nodes with whitespace-only content. That has been patched too.

web_responsive/static/src/js/web_responsive.js

@@ -217,7 +217,7 @@ odoo.define('web_responsive', function (require) {
          */
         _searchResultsNavigate: function (event) {
             // Exit soon when not navigating results
-            if (this.$search_results.is(":empty")) {
+            if (this.$search_results.html().trim() === "") {
                 // Just in case it is the 1st search
                 this._searchMenusSchedule();
                 return;
@@ -246,7 +246,10 @@ odoo.define('web_responsive', function (require) {
                 break;
             // Other keys trigger a search
             default:
+                // All keys that write a character have length 1
+                if (key.length === 1 || key === "Backspace") {
                     this._searchMenusSchedule();
+                }
                 return;
             }
             // Allow looping on results