[CRITICAL BUG] Client freeze on vehicles

[xfurry]

During the scripting process of Pit of Saron, (see latest commits on SD: https://github.com/scriptdev2/scriptdev2/commits/master), I encountered many client crashes which were happening because of vehicles.

How to reproduce:

1. Pull and build the latest core and SD2
2. Use UDB as database
3. Go to the Pit of Saron instance entrance
4. After entering the instance use the following commands: .gm fly on, .modify aspeed 10
5. Then fly straight to Krick or Tyrannus with full speed (see their location here http://www.wowhead.com/zone=4813)
6. Client will crash at the moment when the vehicle get in the visible range.
7. If I reload the client and reenter the game, I will be restored in the exact point where the client crashed, but everything will work just fine. So I think it's related to the first vehicle load on the map.
   PS. This happened with the patch posted below applied, and it happened almost like every time I tried the scenario above. However it won't happen if the player is saved in the visible range of the vehicle at the first login.

I have a patch which will fix some of the crashes, due to vehicles trying to board dead passenger.
However this will not fix all issues!:

diff --git a/src/game/Spell.cpp b/src/game/Spell.cpp
index 9d72290..7033680 100644
--- a/src/game/Spell.cpp
+++ b/src/game/Spell.cpp
@@ -5876,6 +5876,12 @@ SpellCastResult Spell::CheckCast(bool strict)
             }
             case SPELL_AURA_CONTROL_VEHICLE:
             {
+                if (!m_caster->isAlive())
+                    return SPELL_FAILED_CASTER_DEAD;
+
+                if (!expectedTarget->isAlive())
+                    return SPELL_FAILED_TARGETS_DEAD;
+
                 if (m_caster->HasAuraType(SPELL_AURA_MOUNTED))
                     return SPELL_FAILED_NOT_MOUNTED;

Any feedback is appreciated.