bplist: Fix UID node parsing to match Apple's parser

Apple only allows 32 bit unsigned values for UID nodes. Also the encoding
of the length is different from the encoding used for other node types.
The nibble used to mark the size is 1 less than the actual size of the integer
value data, so 0 means 1 byte length 1 means 2 bytes length, etc.
1 file changed