Corrected blocking when exiting

src/main/java/fr/ill/ics/nscclient/serverconnection/ServerConnection.java

@@ -119,8 +119,10 @@ public class ServerConnection {
 	
 	
 	public boolean serverExists() {
-		serverInstance = ServerInstance.getInstance().getApplicationInstance(serverId);
-		return (serverInstance != null && serverInstance.exists());
+		if (serverInstance == null) {
+			serverInstance = ServerInstance.getInstance().getApplicationInstance(serverId);	
+		}
+		return serverInstance.exists();
 	}