No warning is shown is unfold of CPN fails

[Kenneth Yrke Jørgensen]

If the unfolding of a CPN fails no warning is shown and the GUI is in incosistent state.

To reprocude

create a new color with values a and b

Add place -> transition -> place.
Place 1'a and 1'b in first place.

Add 1'a+1'b on both arcs.

Enter simulation mode:

In console:
Running: C:\Users\kyrke\OneDrive - Aalborg Universitet\Skrivebord\tapaal-cpn-alpha\verifypn-win64.exe --write-unfolded-queries C:\Users\kyrke\AppData\Local\Temp\queryOut12137098704785217038.xml --write-unfolded-net C:\Users\kyrke\AppData\Local\Temp\modelOut3023050558321851526.xml -s OverApprox -r 0 -q 0 -x 1 C:\Users\kyrke\AppData\Local\Temp\modelInUnfold16058319387472814654.tapn C:\Users\kyrke\AppData\Local\Temp\queryInUnfold7785476354377413121.xml
Multiple arcs between a place and a transition is not allowed
 at dk.aau.cs.io.PNMLoader.parseOutputArc(PNMLoader.java:523)
 at dk.aau.cs.io.PNMLoader.parseArc(PNMLoader.java:379)
 at dk.aau.cs.io.PNMLoader.parseTimedArcPetriNet(PNMLoader.java:184)
 at dk.aau.cs.io.PNMLoader.parse(PNMLoader.java:125)
 at dk.aau.cs.io.PNMLoader.load(PNMLoader.java:92)
 at dk.aau.cs.io.PNMLoader.load(PNMLoader.java:81)
 at pipe.gui.UnfoldNet.doInBackground(UnfoldNet.java:187)
 at pipe.gui.UnfoldNet.doInBackground(UnfoldNet.java:40)
 at java.desktop/javax.swing.SwingWorker$1.call(SwingWorker.java:304)
 at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
 at java.desktop/javax.swing.SwingWorker.run(SwingWorker.java:343)
 at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
 at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
 at java.base/java.lang.Thread.run(Thread.java:834)