Don't add write errors into bytecounts

Signed-off-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(cherry picked from commit 00d565cfbe)

apps/s_server.c

@@ -2037,8 +2037,10 @@ static int sv_body(char *hostname, int s, unsigned char *context)
                     ret = 1;
                     goto err;
                 }
-                l += k;
-                i -= k;
+                if (k > 0) {
+                    l += k;
+                    i -= k;
+                }
                 if (i <= 0)
                     break;
             }