Change some "int" variables to "size_t" in ssl3_handshake_mac().

BUG=https://crbug.com/535039

Change-Id: I94d35ae5acee510b1e6874c37f35eddda9906e71
Reviewed-on: https://boringssl-review.googlesource.com/5974
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

ssl/s3_enc.c

diff --git a/ssl/s3_enc.c b/ssl/s3_enc.c
index f1924c0..aa0d717 100644
--- a/ssl/s3_enc.c
+++ b/ssl/s3_enc.c
@@ -334,7 +334,7 @@
 static int ssl3_handshake_mac(SSL *s, int md_nid, const char *sender, int len,
                               uint8_t *p) {
   unsigned int ret;
-  int npad, n;
+  size_t npad, n;
   unsigned int i;
   uint8_t md_buf[EVP_MAX_MD_SIZE];
   EVP_MD_CTX ctx;
@@ -357,9 +357,6 @@
   }
 
   n = EVP_MD_CTX_size(&ctx);
-  if (n < 0) {
-    return 0;
-  }
 
   npad = (48 / n) * n;
   if (sender != NULL) {