Fix some documentation errors

CLA: trivial

Reviewed-by: Tomas Mraz <[email protected]>
Reviewed-by: Paul Dale <[email protected]>
(Merged from openssl#16684)

doc/man3/BIO_s_file.pod

@@ -87,7 +87,7 @@ BIO_s_file() returns the file BIO method.
 BIO_new_file() and BIO_new_fp() return a file BIO or NULL if an error
 occurred.
 
-BIO_set_fp() and BIO_get_fp() return 1 for success or 0 for failure
+BIO_set_fp() and BIO_get_fp() return 1 for success or <=0 for failure
 (although the current implementation never return 0).
 
 BIO_seek() returns the same value as the underlying fseek() function:
@@ -96,7 +96,7 @@ BIO_seek() returns the same value as the underlying fseek() function:
 BIO_tell() returns the current file position.
 
 BIO_read_filename(), BIO_write_filename(), BIO_append_filename() and
-BIO_rw_filename() return 1 for success or 0 for failure.
+BIO_rw_filename() return 1 for success or <=0 for failure.
 
 =head1 EXAMPLES
 
@@ -114,7 +114,7 @@ Alternative technique:
  bio_out = BIO_new(BIO_s_file());
  if (bio_out == NULL)
      /* Error */
- if (!BIO_set_fp(bio_out, stdout, BIO_NOCLOSE))
+ if (BIO_set_fp(bio_out, stdout, BIO_NOCLOSE) <= 0)
      /* Error */
  BIO_printf(bio_out, "Hello World\n");
 
@@ -135,7 +135,7 @@ Alternative technique:
  out = BIO_new(BIO_s_file());
  if (out == NULL)
      /* Error */
- if (!BIO_write_filename(out, "filename.txt"))
+ if (BIO_write_filename(out, "filename.txt") <= 0)
      /* Error */
  BIO_printf(out, "Hello World\n");
  BIO_free(out);