[mutter/wip/carlosg/launcher-environment-checks] core: Check environment variables before giving to GAppLaunchContext

[Carlos Garnacho <carlosg src gnome org>]

commit bf8bc65cc955c893649220bcae9d15c6b36a8383
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon May 6 13:00:09 2019 +0200

    core: Check environment variables before giving to GAppLaunchContext
    
    Depending on the type of session, one or the other might be NULL, which
    is not meant to be handled by these functions. Check for both DISPLAY
    envvars before setting them on the GAppLaunchContext.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/issues/586

 src/core/meta-launch-context.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)
---
diff --git a/src/core/meta-launch-context.c b/src/core/meta-launch-context.c
index eda51514f..984338c1b 100644
--- a/src/core/meta-launch-context.c
+++ b/src/core/meta-launch-context.c
@@ -110,13 +110,24 @@ static void
 meta_launch_context_constructed (GObject *object)
 {
   MetaLaunchContext *context = META_LAUNCH_CONTEXT (object);
+  const char *x11_display, *wayland_display;
 
   G_OBJECT_CLASS (meta_launch_context_parent_class)->constructed (object);
 
-  g_app_launch_context_setenv (G_APP_LAUNCH_CONTEXT (context),
-                               "DISPLAY", getenv ("DISPLAY"));
-  g_app_launch_context_setenv (G_APP_LAUNCH_CONTEXT (context),
-                               "WAYLAND_DISPLAY", getenv ("WAYLAND_DISPLAY"));
+  x11_display = getenv ("DISPLAY");
+  wayland_display = getenv ("WAYLAND_DISPLAY");
+
+  if (x11_display)
+    {
+      g_app_launch_context_setenv (G_APP_LAUNCH_CONTEXT (context),
+                                   "DISPLAY", x11_display);
+    }
+
+  if (wayland_display)
+    {
+      g_app_launch_context_setenv (G_APP_LAUNCH_CONTEXT (context),
+                                   "WAYLAND_DISPLAY", wayland_display);
+    }
 }
 
 static gchar *