Core/Player: Initialize m_WeeklyQuestChanged

Fixes:

==8111== Conditional jump or move depends on uninitialised value(s)
==8111==    at 0xFB7AD2: Player::_SaveWeeklyQuestStatus(Trinity::AutoPtr<Transaction, ACE_Thread_Mutex>&) (Player.cpp:19352)

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

@@ -858,6 +858,8 @@ Player::Player(WorldSession* session): Unit(true), m_achievementMgr(this), m_rep
 
     isDebugAreaTriggers = false;
 
+    m_WeeklyQuestChanged = false;
+
     SetPendingBind(0, 0);
 }