Fix crash when using .NoActionBar theme.

m_activity.getActionBar() returns null when a .NoActionBar theme is
declared in AndroidManifest.xml file

Change-Id: I671891d03913209c3f9f34a6f4dd8894c20de5c2
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/android/jar/src/org/qtproject/qt5/android/QtActivityDelegate.java

@@ -1200,6 +1200,8 @@ public class QtActivityDelegate
 
     private void setActionBarVisibility(boolean visible)
     {
+        if (m_activity.getActionBar() == null)
+            return;
         if (ViewConfiguration.get(m_activity).hasPermanentMenuKey() || !visible)
             m_activity.getActionBar().hide();
         else