Fix logging out when download profile_pic fails

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

instaloader/instaloadercontext.py

@@ -75,10 +75,12 @@ class InstaloaderContext:
         username = self.username
         self._session = self.get_anonymous_session()
         self.username = None
-        yield self
-        self._session.close()
-        self.username = username
-        self._session = session
+        try:
+            yield self
+        finally:
+            self._session.close()
+            self.username = username
+            self._session = session
 
     @property
     def is_logged_in(self) -> bool:

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.