Depending on who you ask, Margaret Keane’s big-eyed children paintings are either a precursor to George Rodrigue’s gallery-accepted Blue Dog paintings or a spiritual forerunner of Thomas Kinkade’s kitsch. Either way, the key point for her new bio-film treatment is that they really were her paintings and not the work of her credit-stealing husband. It is a strange story, but it is told in a disappointingly conventional manner in Tim Burton’s “Big Eyes.”