rand: Fix a bug acquiring a context on windows
rand: Fix a bug acquiring a context on windows

The details can be found in the comment I wrote on the block in question, but
the gist of it is that our usage of the TIB for a stack limit was causing
CryptAcquireContext to fail, so we temporarily get around it by setting the
stack limit to 0.

huonw/rand,arthurprs/rand,ebfull/rand,achanda/rand,bhickey/rand,GrahamDennis/rand,shepmaster/rand,waynenilsen/rand,bluss/rand,retep998/rand