Be stricter with side effects in VERIFY #1485

 249 | +        size_t i_ver;
 250 | +        for (i_ver = 0; i_ver < len; i_ver++) {
 251 | +            SECP256K1_GE_VERIFY(&r[i_ver]);
 252 | +        }
 253 |      }
 254 |  #endif

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  48 | @@ -49,6 +49,10 @@ In addition, libsecp256k1 tries to maintain the following coding conventions:
  49 |  * Operations involving secret data should be tested for being constant time with respect to the secrets (see [src/ctime_tests.c](src/ctime_tests.c)).
  50 |  * Local variables containing secret data should be cleared explicitly to try to delete secrets from memory.
  51 |  * Use `secp256k1_memcmp_var` instead of `memcmp` (see [#823](https://github.com/bitcoin-core/secp256k1/issues/823)).
  52 | +* When a test binary is compiled, the `VERIFY` macro will be defined.
  53 | +  * Use `VERIFY_CHECK(cond)` for assertions. The will only be enabled if `VERIFY` is defined.

---

 265 | @@ -266,11 +266,11 @@ static int secp256k1_ellswift_xswiftec_inv_var(secp256k1_fe *t, const secp256k1_
 266 |          secp256k1_fe_mul(&q, &q, &s);                   /* q = s*(4*(u^3+7)+3*u^2*s) */
 267 |          secp256k1_fe_negate(&q, &q, 1);                 /* q = -s*(4*(u^3+7)+3*u^2*s) */
 268 |          if (!secp256k1_fe_is_square_var(&q)) return 0;
 269 | -        ret = secp256k1_fe_sqrt(&r, &q);                /* r = sqrt(-s*(4*(u^3+7)+3*u^2*s)) */
 270 | +        ret_ver = secp256k1_fe_sqrt(&r, &q);                /* r = sqrt(-s*(4*(u^3+7)+3*u^2*s)) */

---

 286 | @@ -287,8 +287,8 @@ static int secp256k1_ellswift_xswiftec_inv_var(secp256k1_fe *t, const secp256k1_
 287 |      }
 288 |  
 289 |      /* Let w = sqrt(s). */
 290 | -    ret = secp256k1_fe_sqrt(&m, &s);                    /* m = sqrt(s) = w */
 291 | -    VERIFY_CHECK(ret);
 292 | +    ret_ver = secp256k1_fe_sqrt(&m, &s);                    /* m = sqrt(s) = w */

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