fix bug where "follow" failed for empty users (who followed no one)

src/twister.cpp

@@ -1595,10 +1595,9 @@ Value follow(const Array& params, bool fHelp)
         string username = users[u].get_str();
         torrent_handle h = startTorrentUser(username);
 
-        LOCK(cs_twister);
+        if( h.is_valid() ) {
-        if( h.is_valid() && m_users.count(localUser) &&
+            LOCK(cs_twister);
-            !m_users[localUser].m_following.count(username) ) {
+            m_users[localUser].m_following.insert(username);
-                m_users[localUser].m_following.insert(username);
         }
     }