Validate length-encoded integers fit a non-negative int before use as a length

Java cannot support array/List with size bigger than int max value (not unsigned int max value)
ReadableByteBuf.readIntLengthEncodedNotNull() decodes the 8-byte (0xfe) form with return (int) readLong(), a silent 64→32 bit narrowing with no range check.

Goal is to throw a proper error when that occurs.

thanks fg0x0 for reporting