pszKey (PSZ) - input
The name of the key for which the size of the data is to be returned.
If the pszKey parameter is NULL, and if the pszApp parameter is not NULL, the pulDataLen returns the length of the buffer required to hold the enumerated list of key names for that application name, as returned by the PrfQueryProfileString function when its pszKey parameter is NULL, and its pszApp parameter is not NULL.