Fix bug caused by commit a3ae3a8

Problem was that in Terra theme, watched icon was not disappearing
when an unwatched show was selected.

This reverts part of the above mentioned commit that was causing
this problem.

(cherry picked from commit dbf9baa)

mythtv/libs/libmythui/mythuistatetype.cpp

@@ -93,7 +93,7 @@ bool MythUIStateType::DisplayState(const QString &name)
     if (i != m_ObjectsByName.end())
         m_CurrentState = i.value();
     else
-        return false;
+        m_currentState = nullptr;
 
     if (m_CurrentState != old)
     {