Evolvefit crashes with EW theories

Created by: Zaharid

See https://github.com/NNPDF/nnpdf/issues/548#issuecomment-539489524 and related discussion.

@scarrazza do you happen to know why this might be?

@voisey, to facilitate debugging, could you please compile the code with debugging and ASAN enabled and run again. That should give better output:

~/n/nnpdf (master %) $ mkdir bld-debug
~/n/nnpdf (master %) $ cd bld-debug
~/n/n/bld-debug (master) $ cmake .. -DENABLE_ASAN=on -DCMAKE_BUILD_TYPE=debug

You might also want to change this

https://github.com/NNPDF/nnpdf/blob/e9949e569ce9bc2b0d3e5710ee10a078dce3763f/nnpdfcpp/src/nnfit/src/evolgrid.cc#L112

to 5 or so, so it runs faster.