Code 'localizing' the node of an ID (a material, here) was kind of a joke,
setting id.lib to NULL is not enough, by far! Now calling ntreeMakeLocal().
And ntreeMakeLocal was also missing indirect->extern switch for its directly used IDs,
which explains why they were lost after a save/reload.
Note that here again, a big part of this 'localizing' code should be made generic
using library_query stuff, but this is for id-remap, not current master...
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