autotag: fix bug when reading file from stdin.

Another attempt at fixing #2. b216057 had a bug where you couldn't pass
a file through stdin because we tried to read the file twice, which we
can't do if the input is a pipe.

autotagger/autotagger.py

@@ -32,8 +32,7 @@ class Autotagger:
             return
 
         with self.learn.no_bar(), self.learn.no_logging():
-            images = [PILImage.create(file) for file in files]
-            dl = self.learn.dls.test_dl(images, bs=bs)
+            dl = self.learn.dls.test_dl(files, bs=bs)
             batch, _ = self.learn.get_preds(dl=dl)
 
             for scores in batch: