(svn r17151) -Fix [FS#3104] (r13974): A train entering a PBS section through a block signal could cause a train crash if another reservation ending at a safe tile was already present in the section.

src/train_cmd.cpp

@@ -3150,6 +3150,15 @@ bool TryPathReserve(Train *v, bool mark_as_stuck, bool first_tile_okay)
 
 	bool other_train = false;
 	PBSTileInfo origin = FollowTrainReservation(v, &other_train);
+	/* The path we are driving on is alread blocked by some other train.
+	 * This can only happen in certain situations when mixing path and
+	 * block signals or when changing tracks and/or signals.
+	 * Exit here as doing any further reservations will probably just
+	 * make matters worse. */
+	if (other_train && v->tile != origin.tile) {
+		if (mark_as_stuck) MarkTrainAsStuck(v);
+		return false;
+	}
 	/* If we have a reserved path and the path ends at a safe tile, we are finished already. */
 	if (origin.okay && (v->tile != origin.tile || first_tile_okay)) {
 		/* Can't be stuck then. */
@@ -3157,14 +3166,6 @@ bool TryPathReserve(Train *v, bool mark_as_stuck, bool first_tile_okay)
 		ClrBit(v->flags, VRF_TRAIN_STUCK);
 		return true;
 	}
-	/* The path we are driving on is alread blocked by some other train.
-	 * This can only happen when tracks and signals are changed. A crash
-	 * is probably imminent, don't do any further reservation because
-	 * it might cause stale reservations. */
-	if (other_train && v->tile != origin.tile) {
-		if (mark_as_stuck) MarkTrainAsStuck(v);
-		return false;
-	}
 
 	/* If we are in a depot, tentativly reserve the depot. */
 	if (v->track == TRACK_BIT_DEPOT) {