Core/Transports: Fix array overflow

Fix an array overflow in TransportMgr::GeneratePath() spline code.

Valgrind log:
 Invalid read of size 4
  at : G3D::Vector3::operator*(float) const (Vector3.h:650)
  by : Movement::C_Evaluate(G3D::Vector3 const*, float, G3D::Matrix4 const&, G3D::Vector3&) (Spline.cpp:103)
  by : Movement::SplineBase::SegLengthCatmullRom(int) const (Spline.cpp:171)
  by : Movement::SplineBase::SegLength(int) const (in /home/jackpoz/trinity/bin/worldserver)
  by : Movement::Spline<double>::initLengths() (SplineImpl.h:86)
  by : TransportMgr::GeneratePath(GameObjectTemplate const*, TransportTemplate*) (TransportMgr.cpp:125)
  by : TransportMgr::LoadTransportTemplates() (TransportMgr.cpp:78)
 Address 0x1d07d154  is 8 bytes after a block of size 300 alloc'd