[fix] prevent a NPE if openrocket does not detect the example files

swing/src/net/sf/openrocket/gui/main/ExampleDesignFile.java

@@ -50,11 +50,14 @@ public class ExampleDesignFile implements Comparable<ExampleDesignFile> {
 			logger.debug("Cannot find jar file, trying to load from directory");
 			designs = getDirFileNames();
 		}
-		if (designs == null || designs.length == 0) {
-			return null;
+
+		if (designs == null ){
+			return new ExampleDesignFile[0];
+		}
+
+		if( 0 < designs.length ) {
+			Arrays.sort(designs);
 		}
-		
-		Arrays.sort(designs);
 		
 		return designs;
 	}