Adding missing BN_CTX_(start/end) in crypto/ec/ec_key.c

RT#4363

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Stephen Henson <steve@openssl.org>

crypto/ec/ec_key.c

@@ -399,8 +399,9 @@ int EC_KEY_set_public_key_affine_coordinates(EC_KEY *key, BIGNUM *x,
     }
     ctx = BN_CTX_new();
     if (ctx == NULL)
-        goto err;
+        return 0;
 
+    BN_CTX_start(ctx);
     point = EC_POINT_new(key->group);
 
     if (point == NULL)
@@ -455,6 +456,7 @@ int EC_KEY_set_public_key_affine_coordinates(EC_KEY *key, BIGNUM *x,
     ok = 1;
 
  err:
+    BN_CTX_end(ctx);
     BN_CTX_free(ctx);
     EC_POINT_free(point);
     return ok;