Core/Misc: Fix some issues detected by static analysis

* Assignment of function parameter has no effect outside the function. Did you forget dereferencing it?
  -> This argument is passed by value, it makes no sence so set it to null here.

* Member variable 'instance_violet_hold_InstanceMapScript::bWiped' is not initialized in the constructor.

(cherry picked from commit 433bc289c2)

src/server/scripts/Northrend/VioletHold/instance_violet_hold.cpp

@@ -133,6 +133,7 @@ public:
             uiCyanigosaEventTimer = 3 * IN_MILLISECONDS;
 
             bActive = false;
+            bWiped = false;
             bIsDoorSpellCast = false;
             bCrystalActivated = false;
             defenseless = true;