Increase the size of the stack buffer to prevent an overflow.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2721)

crypto/ec/eck_prn.c

diff --git a/crypto/ec/eck_prn.c b/crypto/ec/eck_prn.c
index dd3f857..3e826cb 100644
--- a/crypto/ec/eck_prn.c
+++ b/crypto/ec/eck_prn.c
@@ -238,7 +238,7 @@
                      size_t len, int off)
 {
     size_t i;
-    char str[128];
+    char str[128 + 1 + 4];
 
     if (buf == NULL)
         return 1;