Merge bitcoin-core/secp256k1#1009: refactor: Use (int)&(int) in boolean context to avoid compiler warning

16d1322 refactor: Use (int)&(int) in boolean context to avoid compiler warning (MarcoFalke)

Pull request description:

  This one should *really* be only a refactor with the goal to silence static analysis warnings. clang-14 (trunk) recently added one in commit llvm/llvm-project@f62d18f and I expect other tools will offer similar warnings.

  Follow up to #1006, which was not a refactor.

ACKs for top commit:
  real-or-random:
    ACK 16d1322
  jonasnick:
    ACK 16d1322

Tree-SHA512: c465522ea4ddb58b5974c95bc36423c453e6fcf5948cb32114172113b5244209ceaa9418ec86ebe210390ae5509c2f24a42c41a7353de4cfb8fd063b0d5c0e79

Author: real-or-random

Diff for: src/ecdsa_impl.h

@@ -304,12 +304,12 @@ static int secp256k1_ecdsa_sig_sign(const secp256k1_ecmult_gen_context *ctx, sec
     high = secp256k1_scalar_is_high(sigs);
     secp256k1_scalar_cond_negate(sigs, high);
     if (recid) {
-            *recid ^= high;
+        *recid ^= high;
     }
     /* P.x = order is on the curve, so technically sig->r could end up being zero, which would be an invalid signature.
      * This is cryptographically unreachable as hitting it requires finding the discrete log of P.x = N.
      */
-    return !secp256k1_scalar_is_zero(sigr) & !secp256k1_scalar_is_zero(sigs);
+    return (int)(!secp256k1_scalar_is_zero(sigr)) & (int)(!secp256k1_scalar_is_zero(sigs));
 }
 
 #endif /* SECP256K1_ECDSA_IMPL_H */