Skip output generation if nothing is analyzed

src/main/java/org/extendj/ragdoc/RagDocBuilder.java

@@ -80,6 +80,12 @@ public class RagDocBuilder extends Frontend {
     System.out.println("Analyzing source tree...");
     long start = System.currentTimeMillis();
     int result = super.run(args, reader, parser);
+    if (program.options().hasOption("-version")
+        || program.options().hasOption("-help")
+        || program.options().files().isEmpty()) {
+      // Nothing was analyzed.
+      return result;
+    }
     long time = System.currentTimeMillis() - start;
     System.out.format("Analysis took %.1fs.%n", time / 1000.0);
     try {