msi: The input buffer length is the number of characters excluding the NULL terminator, so fix an off by one error [RESEND]

[Mike McCormack]

James Hawkins wrote:

> Is there anything wrong with this patch?
> 
> This fixes bug 5768.
> http://bugs.winehq.org/show_bug.cgi?id=5768
> 
> Changelog:
> * The input buffer length is the number of characters excluding the
> NULL terminator, so fix an off by one error.

msi_strcpy_to_awstring is used by many functions to return strings, so 
how about a test case?

Mike