SLING-6083 htl-maven-plugin should not fail when source directory not found

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1762917 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/main/java/org/apache/sling/maven/htl/ValidateMojo.java b/src/main/java/org/apache/sling/maven/htl/ValidateMojo.java
index 826b2a4..cdea4ad 100644
--- a/src/main/java/org/apache/sling/maven/htl/ValidateMojo.java
+++ b/src/main/java/org/apache/sling/maven/htl/ValidateMojo.java
@@ -104,8 +104,8 @@
             sourceDirectory = new File(project.getBasedir(), sourceDirectory.getPath());
         }
         if (!sourceDirectory.exists()) {
-            throw new MojoExecutionException(
-                    String.format("Configured sourceDirectory={%s} does not exist.", sourceDirectory.getAbsolutePath()));
+            getLog().info("Source directory does not exist, skipping.");
+            return;
         }
         if (!sourceDirectory.isDirectory()) {
             throw new MojoExecutionException(
@@ -113,7 +113,7 @@
         }
 
         if ( !buildContext.hasDelta(sourceDirectory )) {
-            getLog().info("No files found to validate, skipping");
+            getLog().info("No files found to validate, skipping.");
             return;
         }