- reset player's blocking line on traveling between levels

It's not obvious where we can reset blocking line in a more generic way, and whether it's possible at all, because this member is exposed to scripting

https://forum.zdoom.org/viewtopic.php?t=69747

src/g_level.cpp

@@ -1428,6 +1428,7 @@ void FLevelLocals::StartTravel ()
 			if (Players[i]->health > 0)
 			{
 				pawn->UnlinkFromWorld (nullptr);
+				pawn->BlockingLine = nullptr;
 				int tid = pawn->tid;	// Save TID
 				pawn->SetTID(0);
 				pawn->tid = tid;		// Restore TID (but no longer linked into the hash chain)