Catch and ignore unpickling errors in pip installs

This seems to be caused by an odd behavior related to Flask sessions and
instances of Whoogle installed via pip. I didn't investigate it too
much, since catching and ignoring the result doesn't impact Whoogle
functionality at all (configuration and session values persist as
normal). Since this doesn't affect non-pip instances, I don't believe it
to be a fault within Whoogle itself.

Fixes #765

app/routes.py

@@ -81,7 +81,7 @@ def session_required(f):
                     if isinstance(data, dict) and 'valid' in data:
                         continue
                     invalid_sessions.append(session_path)
-            except (EOFError, FileNotFoundError):
+            except (EOFError, FileNotFoundError, pickle.UnpicklingError):
                 pass
 
         for invalid_session in invalid_sessions: