PVS-Studio warning V605 for PHP

PHP_CLI_API size_t sapi_cli_single_write(....)
{
  ....
  size_t shell_wrote;
  shell_wrote = cli_shell_callbacks.cli_shell_write(....);
  if (shell_wrote > -1) {  //<==
    return shell_wrote;
  }
  ....
}

This suspicious code was found in PHP project by PVS-Studio static code analyzer.
Warning message is:
V605 Consider verifying the expression: shell_wrote > - 1. An unsigned value is compared to the number -1. php_cli.c 266

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