By accident, Michael Kimmelman finds himself at the opening preview of the Venice Biennale. “There are gems to find, although the picking is especially tough this year, the 50th edition of the event. This is the largest, most sprawling and also by far the sloppiest, most uninspired, enervating and passionless biennale that I can recall. The curator, Francesco Bonami, has provided the usual nebulous title, pregnant with meaning but signifying nothing. This time it’s ‘Dreams and Conflicts: The Dictatorship of the Viewer.’ It doesn’t begin to account for the miasma that Mr. Bonami has allowed to be assembled.”