Ensure pop-up is not opened, when tabbing out fast from Combobox (#11436)

Checking that no prior Combobox behavior is broken

* Cleaning-up the code

Adding UI test

* Adding TestBench test

client/src/main/java/com/vaadin/client/ui/VComboBox.java

             if (!waitingForFilteringResponse && suggestionPopup.isAttached()) {
                 showPopup = true;
             }
-            if (showPopup) {
+            // Don't show popup, if is not focused
+            if (showPopup && focused) {
                 suggestionPopup.showSuggestions(currentPage);
             }
 
 
     /** For internal use only. May be removed or replaced in the future. */
     public boolean focused = false;
-
+    /** For internal use only. May be removed or replaced in the future. */
+    public boolean noKeyDownEvents = true;
     /**
      * If set to false, the component should not allow entering text to the
      * field even for filtering.
                 return;
             }
 
+            noKeyDownEvents = false;
             if (suggestionPopup.isAttached()) {
                 if (enableDebug) {
                     debug("Keycode " + keyCode + " target is popup");
 
             // queue this, may be cancelled by selection
             int selectedIndex = suggestionPopup.menu.getSelectedIndex();
-            if (!allowNewItems && selectedIndex != -1) {
+            if (!allowNewItems && selectedIndex != -1
+                    && !currentSuggestions.isEmpty()) {
                 onSuggestionSelected(currentSuggestions.get(selectedIndex));
             } else {
                 dataReceivedHandler.reactOnInputWhenReady(tb.getText());
                 // NOP
                 break;
             default:
-                if (textInputEnabled) {
+                if (textInputEnabled && !noKeyDownEvents) {
                     // when filtering, we always want to see the results on the
                     // first page first.
                     filterOptions(0);
             return;
         }
 
+        noKeyDownEvents = true;
         focused = true;
         updatePlaceholder();
         addStyleDependentName("focus");

uitest/src/main/java/com/vaadin/tests/components/combobox/ComboboxFastTabbingOut.java

+package com.vaadin.tests.components.combobox;
+
+import com.vaadin.annotations.Widgetset;
+import com.vaadin.server.VaadinRequest;
+import com.vaadin.tests.components.AbstractTestUI;
+import com.vaadin.ui.ComboBox;
+
+import java.util.ArrayList;
+
+@Widgetset("com.vaadin.DefaultWidgetSet")
+public class ComboboxFastTabbingOut extends AbstractTestUI {
+    @Override
+    protected void setup(VaadinRequest request) {
+        ComboBox<String> combobox = new ComboBox<>(
+                "Press any letter and tab out fast. The pop-up should stay closed");
+        ArrayList<String> values = new ArrayList<>();
+        values.add("AMERICAN SAMOA");
+        values.add("ANTIGUA AND BARBUDA");
+        values.add("Bali");
+        combobox.setId("firstCombobox");
+        combobox.setItems(values);
+
+        ComboBox<String> combobox2 = new ComboBox<>(
+                "Focusing after tabbing from another CB should not open the pop-up");
+
+        combobox2.setItems("AMERICAN SAMOA", "ANTIGUA AND BARBUDA", "Lake 1",
+                "Lake 2");
+        combobox2.setId("secondCombobox");
+        addComponent(combobox);
+        addComponent(combobox2);
+    }
+
+    @Override
+    protected String getTestDescription() {
+        return "On tabbing out fast, the popup window stays closed";
+    }
+
+    @Override
+    protected Integer getTicketNumber() {
+        return 11354;
+    }
+
+}