javadoc post-process should be skipped when no javadocs have been created

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1536161 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/Javadoc.java

@@ -2447,6 +2447,11 @@ public class Javadoc extends Task {
         if (!postProcessGeneratedJavadocs) {
             return;
         }
+        if (!destDir.isDirectory()) {
+            log("No javadoc created, no need to post-process anything",
+                Project.MSG_VERBOSE);
+            return;
+        }
         final String fixData;
         final InputStream in = getClass()
             .getResourceAsStream("javadoc-frame-injections-fix.txt");