gpgconf: No ENOENT warning with --change-options et al.

* tools/gpgconf-comp.c (retrieve_options_from_program): Check ERRNO
before printing a warning.
--

It is common that a conf files does not exist - thus we should not
print a warning.

GnuPG-bug-id: 2944

BTW: The error messages in gpgconf should be reworked to match those
of the other components.

Signed-off-by: Werner Koch <wk@gnupg.org>

tools/gpgconf-comp.c

@@ -2164,8 +2164,11 @@ retrieve_options_from_program (gc_component_t component, gc_backend_t backend)
 
   config = es_fopen (config_filename, "r");
   if (!config)
-    gc_error (0, errno, "warning: can not open config file %s",
-	      config_filename);
+    {
+      if (errno != ENOENT)
+        gc_error (0, errno, "warning: can not open config file %s",
+                  config_filename);
+    }
   else
     {
       while ((length = es_read_line (config, &line, &line_len, NULL)) > 0)