Bug with doc build

[PierreGtch]

I got this bug:

Extension error (sphinx_gallery.gen_gallery):
Handler <function fill_gallery_conf_defaults at 0x28a1c5f70> for event 'config-inited' threw an exception (exception: process no longer exists (pid=71090))
make: *** [html] Error 2

I first lead was this: sphinx-doc/sphinx#10556
but did not solve.

[bruAristimunha]

Hi @PierreGtch,

In code sprint I found that this is stochastic, for some mysterious reason. If you run it several times, it seems to work. It's only on Mac that we've encountered this problem so far.