Fix memcpy/memmove replacements, minor tweaks

Must ignore pointers on size = 0.

Would like to have these still trigger memory breakpoints, will definitely want to inline that.  Tested, it definitely would be a hit to check every time (which was obvious.)

With all current replacements working, Gods Eater Burst goes from 912% -> 940% or so, on x64.  Probably not as good with fastmem on, didn't try.

-[Unknown]