Add nullptr check for pTFAttacker

[Kenzzer]

Description

This fixes a very rare crash in

source-sdk-2013/src/game/shared/tf/tf_gamerules.cpp

Lines 10659 to 10661 in 39f6dde

	void EconItemInterface_OnOwnerKillEaterEvent_Batched( IEconItemInterface *pEconInterface, class CTFPlayer *pOwner, class CTFPlayer *pVictim, kill_eater_event_t eEventType, int nIncrementValue /*= 1*/ )
	{
	for ( int i = 0; i < pOwner->GetNumWearables(); ++i )

As you can see pOwner is never null checked for. And in very rare instances

source-sdk-2013/src/game/server/tf/tf_player.cpp

Lines 9840 to 9855 in 39f6dde

	CTFWeaponBase *pTFWeapon = GetKilleaterWeaponFromDamageInfo( &info );
	if ( !pTFWeapon )
	{
	// Check Wearable instead like demoshields or manntreads
	CTFWearable *pWearable = dynamic_cast< CTFWearable* >( info.GetWeapon() );
	if ( pWearable )
	{
	EconEntity_OnOwnerKillEaterEvent_Batched( pWearable, pTFAttacker, this, kKillEaterEvent_DamageDealt, info.GetDamage() );
	EconEntity_OnOwnerKillEaterEvent_Batched( pWearable, pTFAttacker, this, kKillEaterEvent_PlayersHit, 1 );
	}
	}
	else
	{
	EconEntity_OnOwnerKillEaterEvent_Batched( pTFWeapon, pTFAttacker, this, kKillEaterEvent_DamageDealt, info.GetDamage() );
	EconEntity_OnOwnerKillEaterEvent_Batched( pTFWeapon, pTFAttacker, this, kKillEaterEvent_PlayersHit, 1 );
	}

That function is called when pTFAttacker is nullptr.

Since pTFAttacker is already null-checked in lot of places inside int CTFPlayer::OnTakeDamage( const CTakeDamageInfo &inputInfo ) let's just add one extra check there (see PR changes).