Fix minor issues regarding last commit

- Close session from InstaloaderContext.anonymous_copy().

- Have graphql_count_per_slidingwindow default value in one place rather than
  three.

instaloader/__main__.py

@@ -271,7 +271,7 @@ def main():
     g_how.add_argument('--user-agent',
                        help='User Agent to use for HTTP requests. Defaults to \'{}\'.'.format(default_user_agent()))
     g_how.add_argument('-S', '--no-sleep', action='store_true', help=SUPPRESS)
-    g_how.add_argument('--graphql-rate-limit', type=int, default=20, help=SUPPRESS)
+    g_how.add_argument('--graphql-rate-limit', type=int, help=SUPPRESS)
     g_how.add_argument('--max-connection-attempts', metavar='N', type=int, default=3,
                        help='Maximum number of connection attempts until a request is aborted. Defaults to 3. If a '
                             'connection fails, it can be manually skipped by hitting CTRL+C. Set this to 0 to retry '

instaloader/instaloader.py

@@ -106,7 +106,7 @@ class Instaloader:
                  compress_json: bool = True,
                  post_metadata_txt_pattern: str = None,
                  storyitem_metadata_txt_pattern: str = None,
-                 graphql_rate_limit: int = 20,
+                 graphql_rate_limit: Optional[int] = None,
                  max_connection_attempts: int = 3):
 
         self.context = InstaloaderContext(sleep, quiet, user_agent, graphql_rate_limit, max_connection_attempts)

instaloader/instaloadercontext.py

@@ -47,7 +47,7 @@ class InstaloaderContext:
     """
 
     def __init__(self, sleep: bool = True, quiet: bool = False, user_agent: Optional[str] = None,
-                 graphql_count_per_slidingwindow: int = 20, max_connection_attempts: int = 3):
+                 graphql_count_per_slidingwindow: Optional[int] = None, max_connection_attempts: int = 3):
 
         self.user_agent = user_agent if user_agent is not None else default_user_agent()
         self._session = self.get_anonymous_session()
@@ -56,8 +56,7 @@ class InstaloaderContext:
         self.quiet = quiet
         self.max_connection_attempts = max_connection_attempts
         self._graphql_page_length = 50
-        self.graphql_count_per_slidingwindow = graphql_count_per_slidingwindow \
-                                               if graphql_count_per_slidingwindow else 20
+        self.graphql_count_per_slidingwindow = graphql_count_per_slidingwindow or 20
         self._root_rhx_gis = None
 
         # error log, filled with error() and printed at the end of Instaloader.main()
@@ -76,6 +75,7 @@ class InstaloaderContext:
         self._session = self.get_anonymous_session()
         self.username = None
         yield self
+        self._session.close()
         self.username = username
         self._session = session