fix dual refresh race condition when doing openFeedArticles() in tablet

mode

AndroidManifest.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="org.fox.ttrss"
-    android:versionCode="134"
-    android:versionName="1.12" >
+    android:versionCode="135"
+    android:versionName="1.13" >
 
     <uses-sdk
         android:minSdkVersion="8"

src/org/fox/ttrss/ArticlePager.java

@@ -169,6 +169,7 @@ public class ArticlePager extends Fragment {
 					} catch (BadParcelableException e) {
 						if (getActivity() != null) {							
 							getActivity().finish();
+							return;
 						}
 					}
 					

src/org/fox/ttrss/HeadlinesFragment.java

@@ -291,8 +291,10 @@ public class HeadlinesFragment extends Fragment implements OnItemClickListener,
 		}
 
 		if (m_articles.size() == 0 || !m_feed.equals(GlobalState.getInstance().m_activeFeed)) {
+			if (m_activity.getSupportFragmentManager().findFragmentByTag(CommonActivity.FRAG_ARTICLE) == null) {
 				refresh(false);
 				GlobalState.getInstance().m_activeFeed = m_feed;
+			}			
 		} else {
 			notifyUpdated();
 		}