Core/Unit: Correct speed calculus when affected by SPELL_AURA_MOD_MINIMUM_SPEED (#18136)

(cherrypicked from 4224259d83c336ef46fa627a8ba0015200a788eb)

sql/updates/world/master/2019_07_30_00_world_2017_02_24_00_world.sql

@@ -0,0 +1,2 @@
+-- Val'kyr Shadowguard (Icecrown Citadel/Lich King, all 4 difficulties)
+UPDATE `creature_template` SET `speed_run`=0.642857 WHERE `entry` IN (36609,39120,39121,39122);

src/server/game/Entities/Unit/Unit.cpp

@@ -8559,7 +8559,11 @@ void Unit::UpdateSpeed(UnitMoveType mtype)
 
     if (float minSpeedMod = (float)GetMaxPositiveAuraModifier(SPELL_AURA_MOD_MINIMUM_SPEED))
     {
-        float min_speed = minSpeedMod / 100.0f;
+        float baseMinSpeed = 1.0f;
+        if (!GetOwnerGUID().IsPlayer() && !IsHunterPet() && GetTypeId() == TYPEID_UNIT)
+            baseMinSpeed = ToCreature()->GetCreatureTemplate()->speed_run;
+
+        float min_speed = CalculatePct(baseMinSpeed, minSpeedMod);
         if (speed < min_speed)
             speed = min_speed;
     }

src/server/scripts/Northrend/IcecrownCitadel/boss_the_lich_king.cpp

@@ -1436,7 +1436,6 @@ class npc_valkyr_shadowguard : public CreatureScript
                 _events.Reset();
                 me->SetReactState(REACT_PASSIVE);
                 DoCast(me, SPELL_WINGS_OF_THE_DAMNED, false);
-                me->SetSpeedRate(MOVE_FLIGHT, 0.642857f);
             }
 
             void IsSummonedBy(Unit* /*summoner*/) override