Core/MovementGenerator: Fix crash in taxi paths

Fix a crash in taxi paths happening when joining a battleground/dungeon while on a taxi path after second last node but close to last node, then leaving/finishing the battleground.

(cherry picked from commit 680e1cbd6cf7c52abe104fb87d8fa6dba83fb633)

src/server/game/Movement/MovementGenerators/FlightPathMovementGenerator.cpp

@@ -97,7 +97,7 @@ bool FlightPathMovementGenerator::DoUpdate(Player* owner, uint32 /*diff*/)
         return false;
 
     uint32 pointId = owner->movespline->currentPathIdx() < 0 ? 0 : owner->movespline->currentPathIdx();
-    if (pointId > _currentNode)
+    if (pointId > _currentNode && _currentNode < _path.size())
     {
         bool departureEvent = true;
         do
@@ -116,7 +116,7 @@ bool FlightPathMovementGenerator::DoUpdate(Player* owner, uint32 /*diff*/)
                 }
             }
 
-            if (pointId == _currentNode)
+            if (pointId >= _currentNode)
                 break;
 
             if (_currentNode == _preloadTargetNode)