fix: signal group NPE

Author: IThundxr

src/main/java/com/simibubi/create/content/trains/graph/EdgeData.java

@@ -107,6 +107,8 @@ public UUID getGroupAtPosition(TrackGraph graph, double position) {
 		if (!hasSignalBoundaries())
 			return getEffectiveEdgeGroupId(graph);
 		SignalBoundary firstSignal = next(EdgePointType.SIGNAL, 0);
+		if (firstSignal == null)
+			return null;
 		UUID currentGroup = firstSignal.getGroup(edge.node1);
 
 		for (TrackEdgePoint trackEdgePoint : getPoints()) {

src/main/java/com/simibubi/create/content/trains/graph/TrackGraph.java

@@ -505,7 +505,7 @@ public void resolveIntersectingEdgeGroups(Level level) {
 
 				SignalEdgeGroup group = Create.RAILWAYS.signalEdgeGroups.get(groupId);
 				SignalEdgeGroup otherGroup = Create.RAILWAYS.signalEdgeGroups.get(otherGroupId);
-				if (group == null || otherGroup == null)
+				if (group == null || otherGroup == null || groupId == null || otherGroupId == null)
 					continue;
 
 				intersection.groupId = groupId;