Remove assert from UpdateSignalsOnSegment that globset is empty

Just do the right thing if it isn't empty instead of asserting

src/pbs.cpp

@@ -241,9 +241,7 @@ void UnreserveRailTrack(TileIndex tile, Track t)
 					if (IsTunnelBridgePBS(tile)) {
 						SetTunnelBridgeExitSignalState(tile, SIGNAL_STATE_RED);
 					} else {
-						UpdateSignalsInBufferIfOwnerNotAddable(GetTileOwner(tile));
-						AddSideToSignalBuffer(tile, INVALID_DIAGDIR, GetTileOwner(tile));
-						UpdateSignalsInBuffer();
+						UpdateSignalsOnSegment(tile, INVALID_DIAGDIR, GetTileOwner(tile));
 					}
 				}
 				MarkBridgeOrTunnelDirtyOnReservationChange(tile, VMDF_NOT_MAP_MODE);

src/signal.cpp

@@ -822,9 +822,10 @@ void AddSideToSignalBuffer(TileIndex tile, DiagDirection side, Owner owner)
  */
 SigSegState UpdateSignalsOnSegment(TileIndex tile, DiagDirection side, Owner owner)
 {
-	assert(_globset.IsEmpty());
+	UpdateSignalsInBufferIfOwnerNotAddable(owner);
 	_globset.Add(tile, side);
 
+	_last_owner = INVALID_OWNER;
 	return UpdateSignalsInBuffer(owner);
 }