To celebrate this year’s fiftieth anniversary season, Lincoln Center’s Mostly Mozart charged International Contemporary Ensemble with performing fifty new pieces over the course of the festival. Numbers 45-49 were presented at Merkin Hall on Tuesday, August 23rd. The fiftieth, music by Tyshawn Sorey celebrating Joséphine Baker, was slated for the 24th.   Tuesday’s program consisted entirely of concertos. In some cases, the composers used the term rather loosely, creating amorphously constructed entities rather than the formally distinct works one might expect in the genre. Nearly all were longer than their advertised times: starting at 7:30 PM, the first half alone