Pointed out by Dan Kegel.

kernel32: Fix uninitialised memory read in GetPrivateProfileStringA if GetPrivateProfileStringW returns 0.

The buffer that was passed into the function will remain
uninitialised. Fix reading from this by only reading retW characters
from bufferW and manually nul-terminating the string.

The memory needs to be initialised since NDR will look at the memory
to see if it needs to allocate memory for embedded pointers.

The parameter isn't automatically converted by DispCallFunc, so make
sure we pass in the correct size of memory for the function to store
its BSTR in.

strgtable needs to be an array of the same size as str, including the
nul-terminator.