uploads: autotag animated_gif/png during upload.

Move animated_gif / animated_png autotagging to take place during
uploading, instead of during tag editing. We can't generally assume the
file will be present on the local filesystem after uploading.

app/logical/apng_inspector.rb

@@ -86,7 +86,7 @@ class APNGInspector
     end
 
     @corrupted = !read_success || actl_corrupted
-    return !@corrupted
+    self
   end
 
   def corrupted?
@@ -109,4 +109,4 @@ class APNGInspector
       return framedata.unpack("N".freeze)[0]
     end
 
-end
+end