Fix bssl rand -hex.

It emits NULs instead of c.

Change-Id: Id7f103eac049129dbf9a3e852454b22134ce3270
Reviewed-on: https://boringssl-review.googlesource.com/7220
Reviewed-by: Adam Langley <agl@google.com>

tool/rand.cc

diff --git a/tool/rand.cc b/tool/rand.cc
index 10078e2..3701748 100644
--- a/tool/rand.cc
+++ b/tool/rand.cc
@@ -71,7 +71,7 @@
     }
     RAND_bytes(buf, todo);
     if (hex) {
-      static const char hextable[] = "0123456789abdef";
+      static const char hextable[16 + 1] = "0123456789abcdef";
       for (unsigned i = 0; i < todo; i++) {
         hex_buf[i*2] = hextable[buf[i] >> 4];
         hex_buf[i*2 + 1] = hextable[buf[i] & 0xf];