Two.
The first came on February 4, 2002, in a game against the Minnesota Timberwolves:
http://scores.espn.go.com/nba/recap?gameId=220204024
The second one came on April 15, 2007, in a game against the Dallas Mavericks:
http://scores.espn.go.com/nba/recap?gameId=270415006
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