Today’s musicians would do well by their careers in reading Jim Windolf’s exquisite new book, “ Where the Music Had to Go : How Bob Dylan and the Beatles Changed Each Other—and the World.” In the book’s finest moments, Windolf reminds us what it means both to be an artist and to embrace change. In their day, Dylan and The Beatles challenged each other not only to eschew taking their own inherent greatness for granted, but to accept the risks that being a true artist demands. And that risk — more often than not — is embedded in change. Windolf’s narration of Dylan and The Beatles’ evolving relationship — an association that began even before they famously met in person in a New York City hotel room in August 1964 — is worth the price of admission in and of itself. By the time that they met in the Delmonico Hotel on that fateful evening, Dylan exerted a powerful influence upon The Beatles’ songwriterly aesthetic.…