[metacity] main: check g_setenv return value

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 6066b452731ff22a7ac7b75b91cbc233be00a498
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Mar 14 22:44:12 2021 +0200

    main: check g_setenv return value
    
    Coverity CID: #1502679

 src/core/main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/src/core/main.c b/src/core/main.c
index 038398eda..522022078 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -383,7 +383,10 @@ meta_select_display (gchar *display_name)
     env_var = g_getenv ("METACITY_DISPLAY");
 
   if (env_var)
-    g_setenv ("DISPLAY", env_var, TRUE);
+    {
+      if (!g_setenv ("DISPLAY", env_var, TRUE))
+        g_warning ("Couldn't set DISPLAY");
+    }
 }
 
 static void