Set exitCode=-1 in case of unexpected exception

src/main/java/fr/ill/ics/client/control/MainWindow.java

@@ -192,6 +192,7 @@ public class MainWindow implements ServerConfigurationChangeListener, ServerEnde
 		} catch (Throwable e) {
 			System.err.println("Unexpected exception");
 			e.printStackTrace();
+			exitCode = -1;
 
 		} finally {