fix segfault that could be caused by merging an empty bloom-filter
with a bloom-filter already containing values.

I assume that it is ok to merge an empty bloom-filter with any bloom-filter -
if not we have to change the patch to return an error in this case.
Merge remote-tracking branch 'origin/fastpath'

Slightly adapted after discussing with Bernhard. I also added one
further check.

* origin/fastpath:
  fix segfault that could be caused by merging an empty bloom-filter with a bloom-filter already containing values.
Updating submodule(s).

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Updating submodule(s).

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