Fix logging out when download profile_pic fails

Add try-finally-block to InstaloaderContext.anonymous_copy().
Fixes #159.

instaloader/instaloadercontext.py

@@ -75,7 +75,9 @@ class InstaloaderContext:
         username = self.username
         self._session = self.get_anonymous_session()
         self.username = None
+        try:
             yield self
+        finally:
             self._session.close()
             self.username = username
             self._session = session

instaloader/structures.py

@@ -552,6 +552,8 @@ class Profile:
     @property
     def has_viewable_story(self) -> bool:
         """
+        .. deprecated:: 4.0.6
+
         Some stories are private. This property determines if the :class:`Profile`
         has at least one story which can be viewed using the associated :class:`InstaloaderContext`,
         i.e. the viewer has privileges to view it.