Do not register focus listener for null view in QtEmbeddedDelegate

A null view can not be focused.

Pick-to: 6.7
Change-Id: I0564dd554a304e2e60e3ae83c4782ac348edcd9b
Reviewed-by: Tinja Paavoseppä <tinja.paavoseppa@qt.io>

src/android/jar/src/org/qtproject/qt/android/QtEmbeddedDelegate.java

@@ -135,7 +135,8 @@ class QtEmbeddedDelegate extends QtActivityDelegateBase implements QtNative.AppS
 
     void setView(QtView view) {
         m_view = view;
-        registerGlobalFocusChangeListener(m_view);
+        if (m_view != null)
+            registerGlobalFocusChangeListener(m_view);
     }
 
     public void setRootWindowRef(long ref) {