Fix resource leak in MarkdownFormatter

Change-Id: I156a763291259799ab7fc7c373e80c3fa61b375e
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-server/src/main/java/com/google/gerrit/server/documentation/MarkdownFormatter.java

@@ -136,8 +136,12 @@ public class MarkdownFormatter {
     InputStream in = url.openStream();
     try {
       TemporaryBuffer.Heap tmp = new TemporaryBuffer.Heap(128 * 1024);
+      try {
         tmp.copy(in);
         return new String(tmp.toByteArray(), "UTF-8");
+      } finally {
+        tmp.close();
+      }
     } finally {
       in.close();
     }