[9961] Improved Drain Soul crash

[The_Game_Master]

Current rev: 9973

Description: This crash appeared after http://github.com/mangos/mangos/commit/31264954a46d15f89e02f4a38605251dac37c40b was added. I got it every few hours.

Program received signal SIGSEGV, Segmentation fault.
[switching to Thread 0x7f7498676950 (LWP 20402)]
0x00000000006f8b31 in Aura::PeriodicTick (this=0x4fbaff20)
   at ../../../src/game/SpellAuras.cpp:7189
7189                if (pCaster->GetTypeId() == TYPEID_PLAYER && m_spellProto->SpellFamilyName == SPELLFAMILY_WARLOCK && m_spellProto->SpellFamilyFlags
& UI64LIT(0x0000000000004000))

I temp reverted this commit and works ok.

[VladimirMangos]

I not see how it can crash at this line after "pCaster->DealDamage(m_target"

[The_Game_Master]

I think the crash it's triggered from Unit.cpp since was working fine before.

[zergtmn]

Not related to this bug, but when Drain Soul misses only debuff aura isn't applied, player buff is applied and animation starts anyway.