input: Write a function to generate an HTML table displaying the top 10 bestselling books in a specific genre from a SQLite database. The function should take the genre name as input and return the HTML table as a string. If the genre is not found in the database, return an empty string.
  assert generate_bestseller_table('Fantasy')=='<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Title1</td><td>Author1</td><td>Fantasy</td><td>500</td></tr><tr><td>Title2</td><td>Author2</td><td>Fantasy</td><td>400</td></tr><tr><td>Title3</td><td>Author3</td><td>Fantasy</td><td>300</td></tr></table>'
  assert generate_bestseller_table('Mystery')=='<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>MysteryTitle1</td><td>MysteryAuthor1</td><td>Mystery</td><td>450</td></tr><tr><td>MysteryTitle2</td><td>MysteryAuthor2</td><td>Mystery</td><td>350</td></tr></table>'
  assert generate_bestseller_table('NonexistentGenre')==''
output: def generate_bestseller_table(genre):
      import sqlite3
      conn = sqlite3.connect('books.db')
      cursor = conn.cursor()
      cursor.execute("SELECT Title, Author, Genre, Sales FROM books WHERE Genre=? ORDER BY Sales DESC LIMIT 10", (genre,))
      rows = cursor.fetchall()
      conn.close()
      
      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