Core/Movement: enable item use and spell cast when dismounting

Remove error message and allow spell cast or item use from
mounted state on ground, especially when sitting on
a landed flying mount. Current behavior is that the player
will get the error message "You can't do that while moving"
when trying to cast a spell or pick up an item
while sitting on a flying mount after having landed.

By joschiwald, closes #6236

(cherry picked from commit 19aac66bc262a835cae288fc3d0ccdc8e93d0fb9)

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

@@ -15257,14 +15257,9 @@ bool Unit::SetDisableGravity(bool disable)
     {
         AddUnitMovementFlag(MOVEMENTFLAG_DISABLE_GRAVITY);
         RemoveUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_SPLINE_ELEVATION);
-        SetFall(false);
     }
     else
-    {
         RemoveUnitMovementFlag(MOVEMENTFLAG_DISABLE_GRAVITY);
-        if (!HasUnitMovementFlag(MOVEMENTFLAG_CAN_FLY))
-            SetFall(true);
-    }
 
     static OpcodeServer const gravityOpcodeTable[2][2] =
     {
@@ -15337,14 +15332,9 @@ bool Unit::SetCanFly(bool enable)
     {
         AddUnitMovementFlag(MOVEMENTFLAG_CAN_FLY);
         RemoveUnitMovementFlag(MOVEMENTFLAG_SWIMMING | MOVEMENTFLAG_SPLINE_ELEVATION);
-        SetFall(false);
     }
     else
-    {
         RemoveUnitMovementFlag(MOVEMENTFLAG_CAN_FLY | MOVEMENTFLAG_MASK_MOVING_FLY);
-        if (!IsLevitating())
-            SetFall(true);
-    }
 
     static OpcodeServer const flyOpcodeTable[2][2] =
     {

src/server/game/Movement/MotionMaster.cpp

@@ -473,8 +473,11 @@ void MotionMaster::MoveFall(uint32 id /*=0*/)
     if (std::fabs(_owner->GetPositionZ() - tz) < 0.1f)
         return;
 
+    _owner->SetFall(true);
+
+    // don't run spline movement for players
     if (_owner->GetTypeId() == TYPEID_PLAYER)
-        _owner->SetFall(true);
+        return;
 
     Movement::MoveSplineInit init(_owner);
     init.MoveTo(_owner->GetPositionX(), _owner->GetPositionY(), tz, false);

src/server/game/Spells/Auras/SpellAuraEffects.cpp

@@ -2611,10 +2611,9 @@ void AuraEffect::HandleAuraAllowFlight(AuraApplication const* aurApp, uint8 mode
             return;
     }
 
-    target->SetCanFly(apply);
-
-    if (!apply && target->GetTypeId() == TYPEID_UNIT && !target->IsLevitating())
-        target->GetMotionMaster()->MoveFall();
+    if (target->SetCanFly(apply))
+        if (!apply && !target->IsLevitating())
+            target->GetMotionMaster()->MoveFall();
 }
 
 void AuraEffect::HandleAuraWaterWalk(AuraApplication const* aurApp, uint8 mode, bool apply) const
@@ -3021,10 +3020,9 @@ void AuraEffect::HandleAuraModIncreaseFlightSpeed(AuraApplication const* aurApp,
         // do not remove unit flag if there are more than this auraEffect of that kind on unit on unit
         if (mode & AURA_EFFECT_HANDLE_SEND_FOR_CLIENT_MASK && (apply || (!target->HasAuraType(SPELL_AURA_MOD_INCREASE_MOUNTED_FLIGHT_SPEED) && !target->HasAuraType(SPELL_AURA_FLY))))
         {
-            target->SetCanFly(apply);
-
-            if (!apply && target->GetTypeId() == TYPEID_UNIT && !target->IsLevitating())
-                target->GetMotionMaster()->MoveFall();
+            if (target->SetCanFly(apply))
+                if (!apply && !target->IsLevitating())
+                    target->GetMotionMaster()->MoveFall();
         }
 
         //! Someone should clean up these hacks and remove it from this function. It doesn't even belong here.