[glib] glog: fix crash on windows with --subsystem,windows app

[Matthias Clasen <matthiasc src gnome org>]

commit 615b847d981323477b507d39a736df9652d9b905
Author: Marc-André Lureau <marcandre lureau redhat com>
Date:   Thu Oct 6 17:16:48 2016 +0400

    glog: fix crash on windows with --subsystem,windows app
    
    A windows application compiled with -Wl,--subsystem,windows has no
    console attached. When started from the start menu for ex, it will crash
    when a function attempt to use g_log:
    
     #10 0x00a21b26 in g_logv (log_domain=0xa842e1 <__func__.7668+329> "GLib", 
log_level=G_LOG_LEVEL_CRITICAL, format=0xa845c6 <__func__.7668+1070> "%s: assertion '%s' failed", 
args=0x28f2bc "PG"")
     #11 0x00a21bb1 in g_log (log_domain=0xa842e1 <__func__.7668+329> "GLib", log_level=G_LOG_LEVEL_CRITICAL, 
format=0xa845c6 <__func__.7668+1070> "%s: assertion '%s' failed") at gmessages.c:1337
     #12 0x00a22bac in g_return_if_fail_warning (log_domain=0xa842e1 <__func__.7668+329> "GLib", 
pretty_function=0xa84750 <__func__.65002> "g_log_writer_supports_color",
         expression=0xa844de <__func__.7668+838> "output_fd >= 0") at gmessages.c:2453
     #13 0x00a2239e in g_log_writer_supports_color (output_fd=-2) at gmessages.c:1826
     #14 0x00a226ac in g_log_writer_standard_streams (log_level=G_LOG_LEVEL_WARNING, fields=0x28f3c8, 
n_fields=4, user_data=0x0) at gmessages.c:2254
     #15 0x00a2290e in g_log_writer_default (log_level=G_LOG_LEVEL_WARNING, fields=0x28f3c8, n_fields=4, 
user_data=0x0) at gmessages.c:2357
    
    According to https://msdn.microsoft.com/en-us/library/zs6wbdhx.aspx:
    
    If stdout or stderr is not associated with an output stream (for
    example, in a Windows application without a console window), the file
    descriptor returned is -2. In previous versions, the file descriptor
    returned was -1. This change allows applications to distinguish this
    condition from an error.
    
    Check if the stream exists and has an associated descriptor and return
    G_LOG_WRITER_UNHANDLED if it's not the case.
    
    Fixes:
    https://bugzilla.gnome.org/show_bug.cgi?id=772511
    
    Signed-off-by: Marc-André Lureau <marcandre lureau redhat com>

 glib/gmessages.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/glib/gmessages.c b/glib/gmessages.c
index 8fc33c4..8f45c3d 100644
--- a/glib/gmessages.c
+++ b/glib/gmessages.c
@@ -2251,6 +2251,9 @@ g_log_writer_standard_streams (GLogLevelFlags   log_level,
   g_return_val_if_fail (n_fields > 0, G_LOG_WRITER_UNHANDLED);
 
   stream = log_level_to_file (log_level);
+  if (!stream || fileno (stream) < 0)
+    return G_LOG_WRITER_UNHANDLED;
+
   out = g_log_writer_format_fields (log_level, fields, n_fields,
                                     g_log_writer_supports_color (fileno (stream)));
   _g_fprintf (stream, "%s\n", out);