HBO’s “The Nevers” drops at a time when its existence will have to fight a more intense battle than anything on-screen against the stories about its creator, Joss Whedon. While the man behind “Buffy the Vampire Slayer,” “Angel,” and “Dollhouse” left the show in November as stories about his on-set behavior on “Justice League” were just starting to surface, his fingerprints are all over the four episodes of the new series.