You have access to a node.js function `readLines(fd, position, numLines)` where fd is an open file descriptor, position is the byte offset into the file where to begin reading, and numLines is the maximum number of lines to read, and the function returns [lines, endPosition], where lines is an array containing each line read and endPosition is the offset into the file which is right after the last character read (or is the end of the file). Using this function, write a function called `countLines(fd)` which receives an open file descriptor and return the number of lines the file has