Fix bn_gcd code to check return value when calling BN_one()

BN_one() uses the expand function which calls malloc which may fail.
All other places that reference BN_one() check the return value.

The issue is triggered by a memory allocation failure.
Detected by PR openssl#18355

Reviewed-by: Tomas Mraz <[email protected]>
Reviewed-by: Paul Dale <[email protected]>
(Merged from openssl#18697)

Author: slontis

crypto/bn/bn_gcd.c

@@ -47,7 +47,8 @@ BIGNUM *bn_mod_inverse_no_branch(BIGNUM *in,
     if (R == NULL)
         goto err;
 
-    BN_one(X);
+    if (!BN_one(X))
+        goto err;
     BN_zero(Y);
     if (BN_copy(B, a) == NULL)
         goto err;
@@ -235,7 +236,8 @@ BIGNUM *int_bn_mod_inverse(BIGNUM *in,
     if (R == NULL)
         goto err;
 
-    BN_one(X);
+    if (!BN_one(X))
+        goto err;
     BN_zero(Y);
     if (BN_copy(B, a) == NULL)
         goto err;