Prevent empty state messages from showing briefly

When we clear a list in onPause(), the proper behavior is that the empty state
message is shown, because the list is indeed empty.

However, we will reload the list content again in onResume(),
so the fix chosen in this commit is to force showing the progress bar
right after clearing the list.

Closes #576

briar-android/src/org/briarproject/android/blogs/MyBlogsFragment.java

@@ -82,6 +82,7 @@ public class MyBlogsFragment extends BaseFragment {
 	public void onResume() {
 		super.onResume();
 		adapter.clear();
+		list.showProgressBar();
 		loadBlogs();
 	}