2 issues about sample_core.cpp

[petitfleur]

1. we have found that the 1e-7 comparison can cause some problems. sometimes it is True, sometimes it is False. like 2 > 2 - 1e-7 is true, 4 > 4 - 1e-7 is false..?
2. it seems that the first element of indptr will not be sampled...?

for (EdgeIDType k = e_search; k > std::max(s_search - 1, e_search - neighs); k--)

[petitfleur]

A problem may arise if sampling is done as follows:
for (EdgeIDType k = e_search - 1; k >= std::max(s_search, e_search - neighs); k--)

e_search actually points to the last neighbor allowed to be sampled. If the loop starts at e_search - 1, it may miss it.