Prevent signed/unsigned warning on VC++

ssl/ssl_locl.h

diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index 0238676..e3cb05e 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -565,7 +565,7 @@
 typedef struct ssl3_buf_freelist_st
 	{
 	size_t chunklen;
-	int len;
+	unsigned int len;
 	struct ssl3_buf_freelist_entry_st *head;
 	} SSL3_BUF_FREELIST;