fix offline crash when browsing category as feed

AndroidManifest.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="org.fox.ttrss"
-    android:versionCode="76"
+    android:versionCode="77"
     android:versionName="0.6.2" >
 
     <uses-sdk android:minSdkVersion="8" />

src/org/fox/ttrss/offline/OfflineHeadlinesFragment.java

@@ -325,7 +325,7 @@ public class OfflineHeadlinesFragment extends Fragment implements OnItemClickLis
 				} else {
 					ft.setVisibility(View.GONE);
 				}				
-			} else {
+			} else if (ft != null) {
 				ft.setVisibility(View.GONE);
 			}