[GUI] Handle Enter and Escape in the search box in Preferences.

(cherry picked from commit 0b5a0a6abb)

src/Gui/Dialogs/DlgPreferencesImp.cpp

@@ -1889,10 +1889,6 @@ void PreferencesSearchController::applyHighlightToWidget(QWidget* widget)
 
 bool PreferencesSearchController::handleSearchBoxKeyPress(QKeyEvent* keyEvent)
 {
-    if (!m_searchResultsList->isVisible() || m_searchResults.isEmpty()) {
-        return false;
-    }
-
     switch (keyEvent->key()) {
         case Qt::Key_Down: {
             // Move selection down in popup, skipping separators