bn/bn_mod.c: harmonize BN_mod_add_quick with original implementation.
New implementation failed to correctly reset r->neg flag. Spotted by
OSSFuzz.
@@ -83,6 +83,7 @@ int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
((volatile BN_ULONG *)tp)[i] = 0;
}
r->top = mtop;
+ r->neg = 0;
if (tp != storage)
OPENSSL_free(tp);
