[NTG-context] node.setglue broken in LuaMetaTeX

[Max Chernoff]

Hi Hans,

Using node.setglue in LuaMetaTeX sets all of the glue components to
zero.

This example:

   \startluacode
       local stretch_order = "stretch_order"
       local shrink_order = "shrink_order"
       if status.luatex_engine == "luametatex" then
           stretch_order = "stretchorder"
           shrink_order  ="shrinkorder"
       end
   
       local glue = node.new "glue"
       print(node.getglue(glue))
       node.setglue(glue, 1, 2, 3, 4, 5)
       print(node.getglue(glue))
       glue.width = 1
       glue.stretch = 2
       glue.shrink = 3
       glue[stretch_order] = 4
       glue[shrink_order] = 5
       print(node.getglue(glue))
       node.setglue(glue, 1, 2, 3, 4, 5)
       print(node.getglue(glue))
   \stopluacode

produces this output in MkIV:

   0       0       0       0       0
   1       2       3       4       5
   1       2       3       4       5
   1       2       3       4       5
   
but this output in MkXL:

   0       0       0       0       0
   0       0       0       0       0
   1       2       3       4       5
   0       0       0       0       0
   
Thanks,
-- Max