Add ',' to be encoded in email headers.

When encoding an email header into UTF-8 the ',' was not handled
correctly.

Change-Id: I6704c200155fb26a07aee6aa07a1681b50e4da4e
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/mail/EmailHeader.java b/gerrit-server/src/main/java/com/google/gerrit/server/mail/EmailHeader.java
index bab1118..f2e89ac 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/mail/EmailHeader.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/mail/EmailHeader.java
@@ -69,7 +69,7 @@
       if (b == ' ') {
         r.append('_');
 
-      } else if (b == '=' || b == '"' || b == '_' || b < ' ' || '~' <= b) {
+      } else if (b == ',' || b == '=' || b == '"' || b == '_' || b < ' ' || '~' <= b) {
         r.append('=');
         r.append(Integer.toHexString((b >>> 4) & 0x0f).toUpperCase());
         r.append(Integer.toHexString(b & 0x0f).toUpperCase());