Fix staffers page when set to 'All' depts

There's no single department set if you're viewing all your assigned departments, which was causing a 500 error.

uber/site_sections/shifts_admin.py

@@ -218,7 +218,8 @@ def staffers(self, session, department_id=None, message=''):
             dept_filter = [] if department_id == None else [  # noqa: E711
                 Attendee.dept_memberships.any(department_id=department_id)]
             attendees = session.staffers(pending=True).filter(*dept_filter).all()
-            requested_count = len([a for a in department.unassigned_explicitly_requesting_attendees if a.is_valid])
+            requested_count = None if not department_id else len(
+                [a for a in department.unassigned_explicitly_requesting_attendees if a.is_valid])
             for attendee in attendees:
                 if session.admin_has_staffer_access(attendee) or department_id:
                     attendee.is_dept_head_here = attendee.is_dept_head_of(department_id) if department_id \

uber/templates/shifts_admin/staffers.html

@@ -40,7 +40,7 @@
   or <a href="mailto:{{ c.ADMIN_EMAIL|email_only }}?bcc={{ emails_with_shifts }}">email staffers with shifts here</a>)<b>:</b>
 <br/> <br/>
 <a href="#attendee_form?id=None" class="btn btn-primary">Add new volunteer</a>
-<a href="../dept_admin/requests?department_id={{ department_id }}" class="btn btn-info" target="_blank">Review membership requests{% if requested_count %} ({{ requested_count }}){% endif %}</a>
+{% if department_id != 'All' %}<a href="../dept_admin/requests?department_id={{ department_id }}" class="btn btn-info" target="_blank">Review membership requests{% if requested_count %} ({{ requested_count }}){% endif %}</a>{% endif %}
 <br/><br/>
 
 <table class="table table-striped datatable">