Core/SpellScripts: fix crash caused my spell_gen_vehicle_scaling. closes #5703 (thx vincent-michael)

src/server/scripts/Spells/spell_generic.cpp

@@ -1312,6 +1312,11 @@ class spell_gen_launch : public SpellScriptLoader
         }
 };
 
+enum VehicleScaling
+{
+    SPELL_GEAR_SCALING      = 66668,
+};
+
 class spell_gen_vehicle_scaling : public SpellScriptLoader
 {
     public:
@@ -1323,7 +1328,7 @@ class spell_gen_vehicle_scaling : public SpellScriptLoader
 
             bool Load()
             {
-                return GetCaster()->GetTypeId() == TYPEID_PLAYER;
+                return GetCaster() && GetCaster()->GetTypeId() == TYPEID_PLAYER;
             }
 
             void CalculateAmount(AuraEffect const* /*aurEff*/, int32& amount, bool& /*canBeRecalculated*/)
@@ -1335,7 +1340,7 @@ class spell_gen_vehicle_scaling : public SpellScriptLoader
                 // TODO: Reserach coeffs for different vehicles
                 switch (GetId())
                 {
-                    case 66668:
+                    case SPELL_GEAR_SCALING:
                         factor = 1.0f;
                         baseItemLevel = 205;
                         break;