pckinfoParent (PMMCKINFO) - input
A parent of a chunk is the enclosing chunk - only RIFF and LIST chunks can be parents. If pckinfoParent is given, it is assumed that pckinfoParent was filled in when mmioDescend was called to descend into the parent chunk, and mmioDescend will only search for and descend into a chunk within the parent chunk. If pckinfoParent is NULL, this restriction is not imposed. mmioDescend checks only if a chunk is past the end of a given parent chunk, not before the beginning of the parent chunk. Also, mmioDescend checks only if the beginning of a chunk is past the end of the parent chunk.