asn1/a_int.c: don't write result if returning error.

Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3192)

crypto/asn1/a_int.c

@@ -202,7 +202,6 @@ static int asn1_get_uint64(uint64_t *pr, const unsigned char *b, size_t blen)
         ASN1err(ASN1_F_ASN1_GET_UINT64, ASN1_R_TOO_LARGE);
         return 0;
     }
-    *pr = 0;
     if (b == NULL)
         return 0;
     for (r = 0, i = 0; i < blen; i++) {