input: Write a function to generate an HTML table displaying information about the top 10 bestselling books in a specific genre. The function should take a connection to an SQLite database and a genre name as inputs, execute a query to retrieve the relevant data, format the data into an HTML table, and return the HTML string.
  assert generate_html_table(conn, 'Fantasy')=='<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Sample Title</td><td>Sample Author</td><td>Fantasy</td><td>100000</td></tr></table>'
  assert generate_html_table(conn, 'Mystery')==''
  assert generate_html_table(conn, 'Non-existent Genre')==''
  assert generate_html_table(conn, '')==''
output: def generate_html_table(conn, genre):
      if not genre:
          return ''
      cursor = conn.cursor()
      cursor.execute("SELECT Title, Author, Genre, Sales FROM Books WHERE Genre=? ORDER BY Sales DESC LIMIT 10", (genre,))
      rows = cursor.fetchall()
      if not rows:
          return ''
      html = '<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr>'
      for row in rows:
          html += f'<tr><td>{row[0]}</td><td>{row[1]}</td><td>{row[2]}</td><td>{row[3]}</td></tr>'
      html += '</table>'
      return html