[gimp] plug-ins: fix setting error message in psd-util.

[Jacob Boerema <jboerema src gnome org>]

commit 670ef6b9a3a6e754a20af2e00a8bb67ccd258d45
Author: Jacob Boerema <jgboerema gmail com>
Date:   Wed May 12 16:41:42 2021 -0400

    plug-ins: fix setting error message in psd-util.

 plug-ins/file-psd/psd-util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/plug-ins/file-psd/psd-util.c b/plug-ins/file-psd/psd-util.c
index 8068d13e39..63f2a7fa97 100644
--- a/plug-ins/file-psd/psd-util.c
+++ b/plug-ins/file-psd/psd-util.c
@@ -171,7 +171,7 @@ static const LayerModeMapping layer_mode_map[] =
 void
 psd_set_error (GError  **error)
 {
-  if (! error)
+  if (! error || ! *error)
     g_set_error (error, G_FILE_ERROR, G_FILE_ERROR_FAILED,
                  _("Error reading data. Most likely unexpected end of file."));