set default file type for -exportpropaut

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@10448 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/prism/PrismSettings.java

@@ -1494,6 +1494,7 @@ public class PrismSettings implements Observer
 			if (i < args.length - 1) {
 				setExportPropAut(true);
 				setExportPropAutFilename(args[++i]);
+				setExportPropAutType("txt");  // default
 				for (Map.Entry<String, String> option : options.entrySet()) {
 				    if (option.getKey().equals("txt")) {
 						setExportPropAutType("txt");