Core/Player: Similarly initialize m_SeasonalQuestChanged

Fixes:

==8111== Conditional jump or move depends on uninitialised value(s)
==8111==    at 0xFB7C42: Player::_SaveSeasonalQuestStatus(Trinity::AutoPtr<Transaction, ACE_Thread_Mutex>&) (Player.cpp:19375)
==8111==    by 0xFB56BA: Player::SaveToDB(bool) (Player.cpp:18898)

src/server/game/Entities/Player/Player.cpp

@@ -860,6 +860,8 @@ Player::Player(WorldSession* session): Unit(true), m_achievementMgr(this), m_rep
 
     m_WeeklyQuestChanged = false;
 
+    m_SeasonalQuestChanged = false;
+
     SetPendingBind(0, 0);
 }