Reset |out_no_inverse| before returning errors in BN_mod_inverse_odd.

This more accurately reflects the documented contract for
|BN_mod_inverse_odd|.

Change-Id: Iae98dabe3943231859eaa5e798d06ebe0231b9f1
Reviewed-on: https://boringssl-review.googlesource.com/9160
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

crypto/bn/gcd.c

@@ -231,6 +231,8 @@ static int bn_mod_inverse_general(BIGNUM *out, int *out_no_inverse,
 
 int BN_mod_inverse_odd(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
                        const BIGNUM *n, BN_CTX *ctx) {
+  *out_no_inverse = 0;
+
   if (!BN_is_odd(n)) {
     OPENSSL_PUT_ERROR(BN, BN_R_CALLED_WITH_EVEN_MODULUS);
     return 0;
@@ -245,8 +247,6 @@ int BN_mod_inverse_odd(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
   int ret = 0;
   int sign;
 
-  *out_no_inverse = 0;
-
   BN_CTX_start(ctx);
   A = BN_CTX_get(ctx);
   B = BN_CTX_get(ctx);