[glib] Check that error exists before trying to set it. Fixes bug #640975.

[Ignacio Casal Quinteiro <icq src gnome org>]

commit 401a4233e492e3a2f83e86300b0004d524280e87
Author: Ignacio Casal Quinteiro <icq gnome org>
Date:   Mon Jan 31 13:34:26 2011 +0100

    Check that error exists before trying to set it. Fixes bug #640975.

 glib/gconvert.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)
---
diff --git a/glib/gconvert.c b/glib/gconvert.c
index 52a3dd8..b363bca 100644
--- a/glib/gconvert.c
+++ b/glib/gconvert.c
@@ -769,13 +769,14 @@ g_convert_with_iconv (const gchar *str,
 	      have_error = TRUE;
 	      break;
 	    default:
-              {
-                int errsv = errno;
-                
-                g_set_error (error, G_CONVERT_ERROR, G_CONVERT_ERROR_FAILED,
-                             _("Error during conversion: %s"),
-                             g_strerror (errsv));
-              }
+	      if (error)
+                {
+                  int errsv = errno;
+
+                  g_set_error (error, G_CONVERT_ERROR, G_CONVERT_ERROR_FAILED,
+                               _("Error during conversion: %s"),
+                               g_strerror (errsv));
+                }
 	      have_error = TRUE;
 	      break;
 	    }