[m-rev.] for post-commit review: fix autopar feedback aborts

[Zoltan Somogyi]

This diff avoids aborts in the feedback/{mandelbrot,mmc} test cases.

For review by Julien, since it seems that it was his change at Christmas
to array.fetch_items that broke these tests. Maybe we should reconsider
testing for out-of-bounds before lo > hi, if it requires workarounds like this.

Zoltan.
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