PVS-Studio warning V555 for OpenSSL

typedef struct ok_struct
{
  ....
  size_t buf_len_save;
  size_t buf_off_save;
  ....
} BIO_OK_CTX;

static int ok_read(BIO *b, char *out, int outl)
{
  ....
  BIO_OK_CTX *ctx;
  ....
  /* copy start of the next block into proper place */
  if(ctx->buf_len_save - ctx->buf_off_save > 0)
  ....
}

This suspicious code was found in OpenSSL project by PVS-Studio static code analyzer.
Warning message is:
V555 The expression of the 'A - B > 0' kind will work as 'A != B'. bio_ok.c 243

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/