Minor changes to avoid undefined behaviour warnings.

Avoid creating a reference from a nullptr.
Avoid trying a malloc and memcpy into a 0 length buffer.
Virtual trains should never be drawn.

src/pathfinder/follow_track.hpp

@@ -236,7 +236,7 @@ protected:
 	/** stores track status (available trackdirs) for the new tile into m_new_td_bits */
 	inline bool QueryNewTileTrackStatus()
 	{
-		CPerfStart perf(*m_pPerf);
+		CPerfStart perf(m_pPerf);
 		if (IsRailTT() && IsPlainRailTile(m_new_tile)) {
 			m_new_td_bits = (TrackdirBits)(GetTrackBits(m_new_tile) * 0x101);
 		} else {