changed the definition of dos_PutUniCode

changed the definition of dos_PutUniCode

the previous definition could result is us overflowing a buffer. The
null termination was always added yet the size returned did not
include the null termination.

the new function takes a BOOL null_terminate, and always returns the
total number of bytes consumed by the string.
(This used to be commit 426c90433396a95033eefcc4af97603abc934221)