[GRASS-git] [OSGeo/grass] abb121: parser: Show error for option file (#1433)

[Vaclav Petras]

  Branch: refs/heads/releasebranch_7_8
  Home:   https://github.com/OSGeo/grass
  Commit: abb1214a83e19684eb98f4794de8a5cb7fb74421
      https://github.com/OSGeo/grass/commit/abb1214a83e19684eb98f4794de8a5cb7fb74421
  Author: Vaclav Petras <wenzeslaus at gmail.com>
  Date:   2021-11-22 (Mon, 22 Nov 2021)

  Changed paths:
    M lib/gis/parser.c

  Log Message:
  -----------
  parser: Show error for option file (#1433)

Show the actual error using errno in G_open_option_file function.
Influences g.list, v.external.out, v.in.ascii.

Users won't have to wonder why the file cannot be created or opened.

strerror(errno) is used in lib/gis. Only POSIX fopen requires errno to be set,
but even on Windows errno should be used to obtain specific error information
on error when using fopen according to docs.