src: Avoid needless checks before calling g_strdup()

src: Avoid needless checks before calling g_strdup()

There are few places where the following pattern occurs:

  if (var)
      other = g_strdup(var);

where @other wasn't initialized before g_strdup(). Checking for
var != NULL is useless in this case, as that's exactly what
g_strdup() does (in which case it returns NULL).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>