Fix handling of double-byte chars for tags, keywords.

Change-Id: I03adc405d087eee5a8735f67525a79357ba6c3d5
diff --git a/src/com/google/doclava/NavTree.java b/src/com/google/doclava/NavTree.java
index cc4f43f..cbe9fee 100644
--- a/src/com/google/doclava/NavTree.java
+++ b/src/com/google/doclava/NavTree.java
@@ -184,7 +184,7 @@
             buf.append("\\u");
             for (int j = 0; i < 4; i++) {
               char x = (char) (c & 0x000f);
-              if (x > 10) {
+              if (x >= 10) {
                 x = (char) (x - 10 + 'a');
               } else {
                 x = (char) (x + '0');