DALLAS — With Celtics center Kristaps Porziu0146u0123is sidelined from these NBA Finals due to a rare leg injury, a torn medial retinaculum that ruled out the 7-foot-2 marksman from Game 3 and perhaps the rest of this series, Boston head coach Joe Mazzulla contemplated how to tweak his lineup for Wednesday night’s 106-99 win against Dallas. There, in his bullpen of bigs, waited Luke Kornet, himself a 7-footer who began his NBA career clipping 3-pointers for the New York Knicks. Mazzulla instead called upon 6-foot-8 Xavier Tillman Sr.