Improve error handling

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

@@ -81,6 +81,9 @@ public class RagDocBuilder extends Frontend {
     System.out.println("Analyzing source tree...");
     long start = System.currentTimeMillis();
     int result = super.run(args, reader, parser);
+    if (result != 0) {
+      return result;
+    }
     if (program.options().hasOption("-version")
         || program.options().hasOption("-help")
         || program.options().files().isEmpty()) {