Change emplace_back to push_back, avoid cast
Change emplace_back to push_back, avoid cast

This is a better fix to the VC++ 2017 warning on emplace_back(0), which
reliable sources (twitter, of course) say is a better choice precisely
to avoid warnings like this. Thanks. Context:

https://twitter.com/MalwareMinigun/status/839354045223481344

This is a better fix than the previous commit.

mwinterb/UIforETW,google/UIforETW,mwinterb/UIforETW,google/UIforETW,ariccio/UIforETW,google/UIforETW,google/UIforETW,MikeMarcin/UIforETW,ariccio/UIforETW,MikeMarcin/UIforETW,ariccio/UIforETW,MikeMarcin/UIforETW,ariccio/UIforETW,mwinterb/UIforETW