Creates a new BSTR containing a specified number of characters from an old BSTR, and frees the old BSTR.
Allocates a new string, copies cchcharacters from the passed string into it, and then appends a null character. Frees the BSTR referenced currently by pbstr, and resets pbstr to point to the new BSTR. If psz is Null, a string of length cch is allocated but not initialized.
The psz string can contain embedded null characters and does not need to end with a Null.
If this function is passed a NULL pointer, there will be an access violation and the program will crash. It is your responsibility to protect this function against NULL pointers.