Fix assertion failure when command triggers PBS tunnel/bridge unreserve

In the case where the signal update buffer is not currently empty

src/pbs.cpp

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

src/signal.cpp

@@ -735,6 +735,18 @@ void UpdateSignalsInBuffer()
 	}
 }
 
+/**
+ * Update signals in buffer if the owner could not be added to the current buffer
+ * Called from 'outside'
+ */
+void UpdateSignalsInBufferIfOwnerNotAddable(Owner owner)
+{
+	if (!_globset.IsEmpty() && !IsOneSignalBlock(owner, _last_owner)) {
+		UpdateSignalsInBuffer(_last_owner);
+		_last_owner = INVALID_OWNER; // invalidate
+	}
+}
+
 
 /**
  * Add track to signal update buffer

src/signal_func.h

@@ -152,5 +152,6 @@ void SetSignalsOnBothDir(TileIndex tile, Track track, Owner owner);
 void AddTrackToSignalBuffer(TileIndex tile, Track track, Owner owner);
 void AddSideToSignalBuffer(TileIndex tile, DiagDirection side, Owner owner);
 void UpdateSignalsInBuffer();
+void UpdateSignalsInBufferIfOwnerNotAddable(Owner owner);
 
 #endif /* SIGNAL_FUNC_H */