Comment to XML conversion: we try not to emit empty <Discussion> elements, but
it is not possible to guarantee that without duplicating logic or buffering
<Discussion> element contents.  So, allow empty <Discussion> elements in schema.

llvm-svn: 163842
diff --git a/clang/bindings/xml/comment-xml-schema.rng b/clang/bindings/xml/comment-xml-schema.rng
index a0329f8..3942903 100644
--- a/clang/bindings/xml/comment-xml-schema.rng
+++ b/clang/bindings/xml/comment-xml-schema.rng
@@ -294,9 +294,9 @@
 
   <define name="Discussion">
     <element name="Discussion">
-      <oneOrMore>
+      <zeroOrMore>
         <ref name="TextBlockContent" />
-      </oneOrMore>
+      </zeroOrMore>
     </element>
   </define>