[gimp] app/dialogs: protect against calling gettext(NULL).

[Jehan <jehanp src gnome org>]

commit aa151a08a06d0a65ae0ba19fcb24f30571004eb3
Author: Érico Rolim <erico erc gmail com>
Date:   Fri Dec 11 23:13:32 2020 -0300

    app/dialogs: protect against calling gettext(NULL).
    
    In gimp_dialog_factory_register_entry(), strings were passed to gettext
    without checking for a NULL pointer. The gettext documentation [1]
    points out that that's undefined behavior, and musl libc's
    implementation of gettext segfaults in that case.
    
    [1] https://www.gnu.org/software/gettext/manual/gettext.html#Interface-to-gettext

 app/dialogs/dialogs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/app/dialogs/dialogs.c b/app/dialogs/dialogs.c
index 32eaf081fd..730e777928 100644
--- a/app/dialogs/dialogs.c
+++ b/app/dialogs/dialogs.c
@@ -538,8 +538,8 @@ dialogs_init (Gimp            *gimp,
   for (i = 0; i < G_N_ELEMENTS (entries); i++)
     gimp_dialog_factory_register_entry (factory,
                                         entries[i].identifier,
-                                        gettext (entries[i].name),
-                                        gettext (entries[i].blurb),
+                                        entries[i].name ? gettext(entries[i].name) : NULL,
+                                        entries[i].blurb ? gettext(entries[i].blurb) : NULL,
                                         entries[i].icon_name,
                                         entries[i].help_id,
                                         entries[i].new_func,