Adjust gtkutil.c to build with gcc (GCC) 11.2.1 with -Wanalyzer-null-argument

[Alexander Kuleshov <kuleshovmail@gmail.com>]

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Hello,

I'm getting:

gtkutil.c: In function ‘xg_item_label_same_p’:
gtkutil.c:2936:54: error: use of NULL where non-null expected
[CWE-476] [-Werror=analyzer-null-argument]
 2936 |                   && ((!old_label && !utf8_label) || strcmp
(utf8_label, old_label) == 0));

error during building of GNU Emacs from master on Fedora 34 with GCC
11.2.1. I've attached a simple fix
for that.

Thank you.

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From f4588402aac1c001b93b2df0de344fa8316276cc Mon Sep 17 00:00:00 2001
From: Alexander Kuleshov <kuleshovmail@gmail.com>
Date: Wed, 1 Sep 2021 16:46:19 +0600
Subject: [PATCH] Fix building with gcc 11.1.2 and -Wanalyzer-null-argument
 option

 * src/gtkutil.c (xg_item_label_same_p): Fix a bug where strcmp could
get NULL as argument
---
 src/gtkutil.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/gtkutil.c b/src/gtkutil.c
index 313cfc82c2..9ac2a6fea3 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -2932,8 +2932,8 @@ xg_item_label_same_p (GtkMenuItem *witem, const char *label)
   char *utf8_label = get_utf8_string (label);
   const char *old_label = witem ? xg_get_menu_item_label (witem) : 0;
 
-  bool is_same = (!old_label == !utf8_label
-		  && (!old_label || strcmp (utf8_label, old_label) == 0));
+  bool is_same = (!old_label == !utf8_label)
+		  || ((old_label && utf8_label) && strcmp (utf8_label, old_label) == 0);
 
   if (utf8_label) g_free (utf8_label);
 
-- 
2.31.1