[gimp] Revert "libgimpconfig: remove more g_assert()."

[Jehan <jehanp src gnome org>]

commit 1ed8ed8223881c93cfd7aca6e0e5b5fa150c92f7
Author: Jehan <jehan girinstud io>
Date:   Thu Feb 10 22:02:31 2022 +0100

    Revert "libgimpconfig: remove more g_assert()."
    
    This reverts commit 40bebec27318c24727d54e286549729b26088bcb.
    
    Actually I was wrong, there was a bug in gimpconfig-deserialize.c. See
    coming commits.

 libgimpconfig/gimpconfig-iface.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/libgimpconfig/gimpconfig-iface.c b/libgimpconfig/gimpconfig-iface.c
index 8052c7e0f5..65e83c4eca 100644
--- a/libgimpconfig/gimpconfig-iface.c
+++ b/libgimpconfig/gimpconfig-iface.c
@@ -539,6 +539,9 @@ gimp_config_deserialize_stream (GimpConfig    *config,
 
   gimp_scanner_unref (scanner);
 
+  if (! success)
+    g_assert (error == NULL || *error != NULL);
+
   return success;
 }
 
@@ -583,6 +586,9 @@ gimp_config_deserialize_string (GimpConfig   *config,
 
   gimp_scanner_unref (scanner);
 
+  if (! success)
+    g_assert (error == NULL || *error != NULL);
+
   return success;
 }