message: secp256k1/src/tests.c:  Properly handle sscanf return value
  Summary:
  This pull request fixes a bug which allows the `sh` variable to be used uninitialized when sscanf returns EOF.
  This is a backport of secp256k1 PR650
  Test Plan:
  ninja check-secp256k1
  Reviewers: #bitcoin_abc, nakihito
diff: @@ -5188,7 +5188,7 @@ int main(int argc, char **argv) {
  const char* ch = argv[2];
  while (pos < 16 && ch[0] != 0 && ch[1] != 0) {
  unsigned short sh;
  - if (sscanf(ch, "%2hx", &sh)) {
  + if ((sscanf(ch, "%2hx", &sh)) == 1) {
  seed16[pos] = sh;
  } else {
  break;
  