[vte] spawn: Don't try to call null callback

[Christian Persch <chpe src gnome org>]

commit f35a9e259d93e1c53cdb6f0439873bf3e85ed934
Author: Christian Persch <chpe src gnome org>
Date:   Fri May 1 10:46:43 2020 +0200

    spawn: Don't try to call null callback

 src/spawn.hh | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/src/spawn.hh b/src/spawn.hh
index da4f3905..5e8ff733 100644
--- a/src/spawn.hh
+++ b/src/spawn.hh
@@ -40,11 +40,11 @@ private:
 
         vte::glib::RefPtr<VtePty> m_pty{};
 
-        vte::glib::StringPtr m_cwd;
-        vte::glib::StringPtr m_fallback_cwd;
-        vte::glib::StringPtr m_arg0;
-        vte::glib::StrvPtr m_argv;
-        vte::glib::StrvPtr m_envv;
+        vte::glib::StringPtr m_cwd{};
+        vte::glib::StringPtr m_fallback_cwd{};
+        vte::glib::StringPtr m_arg0{};
+        vte::glib::StrvPtr m_argv{};
+        vte::glib::StrvPtr m_envv{};
 
         std::vector<vte::libc::FD> m_fds{};
 
@@ -68,7 +68,7 @@ public:
 
         ~SpawnContext()
         {
-                if (m_child_setup_data)
+                if (m_child_setup_data && m_child_setup_data_destroy)
                         m_child_setup_data_destroy(m_child_setup_data);
         }