NeuralNetwork: Occasional crashes when running tests

[josefbehr]

Sometimes, when running the tests, testNeuralNetwork crashes with Signal 6 and dumps a core (can send it to you, since github doesnt support attachments ...). Here's the backtrace: https://gist.github.com/josefbehr/5846553

[cybott]

I also have this occasionally since a long time. Backtraces show a weird location (if(x == 0) { as source of the problem. Since this happens only in the test cases it has a quite low priority to be fixed.